command line terminology: what are these parts of a command called?

The common names for each part is as follows:

┌1┐ ┌──2───┐
git checkout master
│   └──────3──────┘
└───────4─────────┘

1. Command name (first word or token of command line that is not a redirection or variable assignment and after aliases have been expanded).

2. Token, word, or argument to the command. From man bash:

   word: A sequence of characters considered as a single unit by the shell. Also known as a token.

3. Generally: Arguments

4. Command line.

---

The concatenation of two simple commands with a | is a pipe sequence or pipeline:

┌─1┐ ┌──────2──────┐ ┌─2─┐ ┌──2──┐   ┌──1───┐ ┌2┐┌2┐┌2┐┌────2─────┐ ┌2┐ ┌2┐
find transcripts/?.? -name '*.txt' | parallel -- sh -c 'echo $1 $2'  {} {/}
│    └────────────3──────────────┘            └────────────3──────────────┘
└───────────────────────────────────4─────────────────────────────────────┘

Mind that there are redirection and variable assignments also:

┌──5──┐ ┌1┐ ┌─2─┐ ┌─2─┐   ┌───6──┐ ┌1┐ ┌─5─┐
<infile tee file1 file2 | LC_ALL=C cat >file
└─────────7───────────┘   └───────7────────┘
└─────────────────────4────────────────────┘

Where (beside the numbers from above):

5. redirection.
6. Variable assignment.
7. Simple command.

This is not an exaustive list of all the element a command line could have. Such a list is too complex for this short answer.

@isaac's answer above seems good.

I want to extend this with some sources.

I guess the POSIX standard might in some sense be considered canonical. Other sources might be man bash and man proc.

┌1┐ ┌──2───┐
git checkout master
│   └──────3──────┘
└───────4─────────┘

POSIX suggests that:

1. Is the command name (rather than the command, though even this document uses command in places)
2. Argument
3. Arguments
4. Command (though man proc uses the command line)

It also has terminology for many more complicated commands.

I think command is pretty ambiguous so perhaps the term command name and command line are good for clarity.j