From TTWiki

Here you find a list of terms used throughout the NML tutorial with an explanation of their meaning.

Variable added to a block to provide the block with certain information needed for the block to function correctly.
A grouped instruction to do certain things. NML mainly consists from blocks. Block contents are grouped between curly brackets { and }.
Means of telling NML what type of item you want to add or modify. Supplied to certain blocks as argument.
The name of a block or template. All identifiers are self-chosen an must be unique throughout the NML file, even if they are used by different block types. May contain lowercase and uppercase letters A to Z, numbers 0 to 9 and underscore _ but may not start with a number. It's recommended to start an identifier with the name of the block type.
A special user-defined variable. Can be hidden in the NML file or user-configurable through the game's parameter settings.
A single graphic to be used by the game, together with it's blue background. A graphics file can contain multiple sprites.
Special block to allow making sprite definitions variable and reusable.
A named value that can change depending on certain conditions in the game or NML code.