Perimeter and parameter are easily confused words.
The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary, but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted, or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway.
Autocorrect suggests words that start with the same letters. It’s suggesting what word you may want to save time, but quite often, its suggestions are pretty off base. They don’t help you out, but they do make you laugh.
Perimeter (pronounced “per-ihm-uh-turr”) is a noun. It can mean the lines demarcating an area. In geometry, it means the borders of a 2D figure. It can also mean the length of all a polygon’s sides, or the outermost limits of a thing.
Parameter (pronounced “puh-ram-uh-turr”) is a noun. In general, it means a guideline, a boundary, or condition for a project or other undertaking. It can also mean a characteristic or factor that is influential of an outcome.
In mathematics, it means an independent variable in parametric equations, or a variable in a function that determines the form, but not the nature, of the function.
In statistics, a variable in a distribution whose value creates different outcomes in distribution.
In coding, it means a variable that requires a specific value for the execution of a program or a procedure within a program.
The following story uses both words correctly:
Parmenia wanted to redesign her condo before the summer arrived. She sought quotes from a variety of professionals. The interior designers asked for the perimeter measurements of each room. They also asked for project parameters, like her budget, time constraints, and color preferences.