My students, in the past, have had trouble keeping perimeter and area correctly identified. My team partner came up with the following:
As they say the word, PER-I-ME-TER, they are "drawing" a rectangle (or square) in the air. The word has four syllables and the rectangle (or square) has four sides, so they say a syllable as they "draw" a side. ANYTIME we say the word PERIMETER, we automatically draw the rectangle (or square) in the air to indicate that perimeter is the measure of the OUTSIDE of the shape.
After they got that,
I taught them to remember AREA by waving their flattened hand in a small space as if they are filling in the interior of the whole space. They are taught that AREA is the measure of the INSIDE of a shape. Again, each time we say AREA, we wave a flat hand to 'fill in' a small space.
Not sure if this explanation is clear enough

, but this was a great aid in helping my students to remember what each of the terms were, without confusing them.