Direct acyclic graph in which the vertexes are transactions/blocks, and the direct edges are verifications. If vertex A has an edges to vertex B, we say that transaction A verifies transaction B (and indirectly verifies all transactions verified by transaction B).
A special transaction that issues new tokens.
A transaction that has been confirmed by the network and is very unlikely to be voided, i.e., its accumulated weight is above a given threshold.
A transaction that has been successfully verified by other transactions.
A voided transference of funds. Usually transactions are voided because they are verifying other voided transactions or because it is a double-spending transaction with lower accumulated weight.
A transaction is valid when its funds are valid, and it has not been voided. A valid transaction eventually becomes a confirmed transaction.
Transactions that have exactly the same inputs and ouputs. Their hash are different because they may have different parents, different timestamps, or simply different nounces.
The block chain that has the highest score, like the best (or the longest) chain in Bitcoin.
When two or more chains have the same score, they are all best chain candidates.
All chains whose scores are below the score of the best chain.