Backtick

The backtick is a typographical mark used mainly in computing. It is also known as backquote, grave, or grave accent.

The character was designed for typewriters to add a grave accent to a (lower-case) base letter, by overtyping it atop that letter. On early computer systems, however, this physical dead key+overtype function was rarely supported, being functionally replaced by precomposed characters. Consequently, this ASCII symbol was rarely (if ever) used in computer systems for its original aim and became repurposed for many unrelated uses in computer programming.

The sign is located on the left-top of a US or UK layout keyboard, next to the key. Provision (if any) of the backtick on other keyboards varies by national keyboard layout and keyboard mapping. Provided by Wikipedia