In class 7 mathematics ICSE, the topic of perimeter and area of polygons covers the following concepts:

1. **Perimeter**: The perimeter of a polygon is the sum of the lengths of all its sides. For regular polygons (where all sides and angles are equal), the perimeter can be calculated by multiplying the number of sides (n) by the length of each side (s). So, perimeter = n * s.

2. **Area**: The area of a polygon is the measure of the region enclosed by the polygon. The formula for finding the area of different polygons is different:
– For a rectangle: Area = length * width
– For a square: Area = side * side
– For a triangle: Area = 1/2 * base * height
– For a parallelogram: Area = base * height
– For a trapezium: Area = 1/2 * sum of parallel sides * distance between them

3. **Regular and Irregular Polygons**: Regular polygons have all sides and angles equal, making them easier to calculate. Irregular polygons have sides and angles of varying lengths and sizes, making their calculation more complex.

4. **Calculating Perimeter and Area**: To calculate the perimeter and area of a polygon, you need to know the lengths of its sides and, for area, the base and height (if applicable). Following the correct formulas for each type of polygon is crucial for accurate calculations.