A spelling or grammatical mistake in a computer program is called what?

Bugs

In computer lingo, we call programming mistakes 'bugs.'
The process of fixing mistakes is called 'debugging.'
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A bug is any sort of a mistake in a program which causes the program to behave in an unpredictable way and is hard to find. A spelling mistake is not normally considered a bug and does not have any special title.

A grammatical error in language is called a syntax error. This is used in computer programs to refer to an error in the coding, but not when referring to its spelling or grammar.

The term 'bug' comes from the very early days of computers with valves (tubes for the Americans). These ran quite hot and needed ventilation, so real bugs could get in and short-circuit things causing crashes. This was in the days of no monitors, and reels of punched paper tape to input your programme and calculation. Beats me how the things worked at all.

Bugs are commonly errors in logic and become apparent when the program is executed. Syntax errors are closer to grammatical mistakes although not usually spelling mistakes, and are usually discovered when the program is compiled (i.e. before the program is executed).