My (limited) gaming experience
Splinterlands is personally what reconnected me with the gaming world. The last game I used to play avidly was FIFA on my old Xbox 360, which was, to say the least, a while ago.
Given that my "gaming" background was fairly limited when I started playing Splinterlands, most of the following terms were unfamiliar to me.
Thus, I thought this lexicon could be in some ways helpful for future casual players out there or non-native English speakers like me.
NFT: Non-Fungible Tokens
The main aspect that attracted me to this game was the ownership experience. I used to have a hard time wrapping my head around NFTs selling for astronomical prices.
In Splinterlands however, the ownership of NFTs is tightly linked to their utility, which makes it much more straightforward for new investors to understand the space.
I do believe that this is all part of 
The following list of words is mostly focused on the Gaming dimension of the Splinterlands' ecosystem that I wasn't familiar with and not so much on the Blockchain aspect, which would require many more complex concepts that I wouldn't be able to explain in a simple manner.
Splinterlands' Lexicon for Dummies
Quick tip:
You can use the search tool "find in page" of your browser to look for a specific word.
Words covered in this post:
Airdrop, APR, Auto-battle, Auto-bid, BCX, Brawl, Buff, Burn value, CP, Credits, DEC, ECR, EOS, HBD, Hive, Hive-Engine, Hive-Keychain, HP, IGN, Lore, MMR, Nerf, OP, Peakmonsters, RC, RNG, Splinter, SPS, Staking, Tribaldex, Vouchers.
Airdrop
Assets distributed for free to players who have a stake in the game (tokens, cards, and so on).
APR
Annual Percentage Rate
Gains that result from staking tokens, SPS for instance.
See: Staking, SPS.
Auto-battle
The battle runs automatically once both players have chosen their cards. The players cannot influence the outcome after having submitted their team.
Auto-bid
Third-party platforms like Peakmonsters allow players to place bids for renting cards at a chosen cost.
See: Peakmonsters.
BCX
Base Card eXperience
The BCX is the number of cards needed to level up a monster to a desired level.
Brawl
Battles between guilds.
Buff
A card is buffed when it receives upgraded stats from the developers as a way of balancing the game.
See: Nerf.
Burn Value
Each card has an intrinsic value in terms of DEC. The burn value is what the player would get by virtually burning the card.
See: DEC.
CP
Collection Power
This is a central piece of the game. Your CP is the burn value of your entire collection of cards (purchased & rented combined).
See: Burn Value.
Credits
This is the equivalent of fiat currency in the game. One credit equals $0.001 and its value does not fluctuate.
DEC
Dark Energy Crystals
DEC is the main currency in the game. It allows players to buy cards, get revenue from rentals, and so on. Its original pegged value was set at $0.001 as it was intended as a stable coin. However, unlike credits, the value of DEC does fluctuate.
See: Credits.
ECR
Energy Capture Rate
The closer the ECR of a player is to 100%, the more the player will earn DEC from winning battles.
See: DEC.
EOS
End Of Season
A season in Splinterlands lasts roughly 15 days. At the end of each season, players receive rewards according to the league they've reached.
HBD
Hive Backed Dollars
HBD is the stable coin of the Hive blockchain.
See: Hive.
Hive
Blockchain on which Splinterlands has been transferred to.
Hive-Engine
An exchange platform that allows players to swap the in-game tokens with each other or other cryptocurrencies.
See: Hive, Tribaldex.
Hive-Keychain
A safety tool that allows players to confirm transactions within the Hive ecosystem.
See: Hive.
HP
Hive Power
The more Hive tokens players stake, the more Hive Power they get, which in turn increases their Resource Credits (RC) that allow them to interact within the Hive blockchain (buy cards, rent cards, swap tokens, post articles, and so on).
See: Hive, Staking, RC.
IGN
In-Game Name
This is simply your username in the game.
Lore
Short backstories about the characters of the game.
MMR
Match Making Rating
This is the rating you get by battling against other players.
Nerf
A card is nerfed when it gets downgraded stats from the developers as a way of balancing the game.
See: Buff.
OP
OverPowered
A card is overpowered when it is way too powerful compared to other cards.
Peakmonsters
A third-party platform that facilitates many actions within the game (buy, rent, bid, and so on).
RC
Resource Credits
Resource Credits work in the background to allow players to perform transactions within the Hive ecosystem (buy, rent, post, etc).
See: Hive.
RNG
Random Number Generators
In Splinterlands, RNG is mostly the randomness coming from opening booster packs or loot chests.
Splinter
A splinter is a set of cards that belong to the same "family". There are 6 splinters in the game (Fire, Water, Earth, Life, Death, and Dragon).
SPS
Splintershards
SPS is envisioned as a governance token, which will give players a certain degree of control over the future development of the game.
Staking
Staking is similar to locking tokens into a "bank saving account" that allows players to earn interest on it.
Tribaldex
An exchange platform that allows players to swap tokens belonging to the Hive ecosystem with each other and other cryptocurrencies.
See: Hive, Hive-Engine.
Vouchers
Voucher tokens are given to players who stake SPS. Those vouchers' current utility is to redeem bonus Chaos Legion packs or buy Promotional cards.
See: SPS.
If you have other terms in mind, feel free to leave them in the comment section below for others who might stumble upon this post.
Thomas
For new players interested in joining this amazing game, you can support me by using the following referral link (at no extra cost to you!):
https://splinterlands.com?ref=tt88
Thank you.