I’ve seen it take arguments, and apparently there’s a starred version, but I can’t find any documentation because it is ungooglable!
There is no official name for it (at least I don't know of any) and it would be difficult to give it a single short name as the purpose of this command is more or less
A command to separate lines or rows of material (depending on context) while controlling the space between such lines or rows and indicating whether a page break between them is forbidden.
Now turn this into a short word please :-)
The full syntax in standard LaTeX is
] with the
* indicating that a pagebreak is forbidden (it may not be allowed anyway for other reasons) and the dimension defining the extra space to be added between the two rows or lines. Both the
[...] are optional and it is allowed to put spaces between
This is what all environments etc of standard LaTeX use when they make use of this command. The actual code that the command runs depends on the situation, so in a
tabular it technically does something completely different to the situation in a paragraph. See also What does \\* do?
An introduction such as ltshort will cover this command in detail, along with other ungooglable terms.