Because I see a lot of new altcoin enthusiasts joining /r/altcoin, I made a simple glossary with crypto jargon. Do you miss anything? Don't hesitate to add it as a comment (I will edit the post).
Altcoin, the abbreviation for alternative coin, or alternate coin, or all blockchain projects and related currency that exist in addition to Bitcoin.
Bearish, a downward trend.
Block is a part of the Blockchain and is usually associated with an encrypted hash with the previous block in the block.
Blockchain, very neatly explained by Nieuwsuur (or here), but in text: a decentralized database that maintains a data list that can not be manipulated.
BTC (฿). I do not intend to spell out all currencies, but Bitcoin is an exception.
Bullish, an upward trend.
Core wallet, a wallet that contains the whole blockchain and most of the time delivers tools to give developers the ability to program in or on the blockchain.
Dapps aka applications written in the blockchain, which means it's a decentralized application aka Dapp.
Electrum wallet, a light weight wallet to store coins. Doesn’t download the blockchain, but gets the information from a thirth party.
Encryption, data lock that can only be unlocked with a private key.
Exchange, sometimes called coinexchange, is the exchange office where buyers and sellers can trade in Bit and Altcoins. Examples are Litebit, BTCdirect, Kraken and Bittrex.
FOMO means Fear Of Missing Out. As the term suggests, the Bitcoin or an altcoin rises sharply in value and investors take steps without rationale – so emotion – because they are afraid to miss the boat.
FUD stands for Fear, Uncertainty & Doubt. In the world of crypto FUD means spreading fear, uncertainty or doubt about a certain blockchain project.
Hash, an encryption that can no longer be undone.
HODL, either hold, but then written wrong. Reportedly a Bitcointalk user wearing a drunk mood over his keyboard. HODL is currently jargon for long-term investor cryptocurrency trader. Nice acronym mentioned in the comments: Hold On Despite Loss.
ICO, Initial Coin Offering. A crowd sale that offers the opportunity to purchase digital coins from a new blockchain project.
Miner, device validating the blockchain (transactions).
Mining reward, the reward that a miner receives for the computing power he delivers to check the nodes in the blockchain.
Mnemonic Phrase a fancy version of your private key, that is actually used to derive multiple private keys.
Public key, publicly accessible “key”, in crypto currency jargon your wallet.
Private key, the key to open your wallet.
Proof of Stake, verification of the blockchain is done by (wallet) adresses with a certain amount of coins. The more coins means the more authority and computing power for verifying the blockchain.
Proof of Work is roughly a method where blockchain(transactions) are verified with computing power.
Satoshi is the smallest part of a bitcoin. 1 Satoshi = 0.00000001 ฿.
Wallet, a digital wallet on cryptocurrency. Examples are Jaxx, Exodus and the Gulden Wallet.