These two words are often confused, especially parameter for perimeter.
Perimeter, pronounced with a short i in the second syllable, means "the border or line around an object, especially a two-dimensional geometric figure." By extension, it can refer to the border of any area or any kind of limit.
Parameter, pronounced with a short a in the second syllable, is a specific mathematical or physical term which means "a variable which has the same value in more than one equation." Unfortunately, people will often use the word parameter when they mean "boundary" or "limitation," because it sounds more scientific or technical.
Sociologist Thomas Sowell writes: "One of the incidental examples of 'scientific' puffery is the widespread use of the term 'parameters' to mean boundaries, rather than its actual meaning in mathematical equations. What are usually called 'parameters' in discussions of social policies could more accurately be called perimeters. But of course that would not foster the illusion of 'science.'"