It is a bracket. It can also be shown as { } or as a straight line instead of the curly line. My keyboard does not have the straight line version only the curly line version.

That would be an alternate left bracket!

The straight line is a bracket:

[ ]


The curved brackets are called braces:

{ }

Curly Brace

Brace, curly bracket or french bracket, but not plain bracket which are these: []