In Class 6 ICSE Mathematics, the topic of circles and quadrilaterals introduces students to fundamental geometric concepts.

**Circles**: Students learn about the definition of a circle, its various parts like radius, diameter, chord, and circumference. They also study the relationship between the circumference and diameter (π = C/d), and how to calculate the circumference and area of a circle using formulas (C = 2πr, A = πr²).

**Quadrilaterals**: The topic covers different types of quadrilaterals such as squares, rectangles, parallelograms, rhombuses, and trapeziums. Students learn to identify the properties of these quadrilaterals, including their sides, angles, diagonals, and symmetry. They also study the formulas to calculate the perimeter and area of these shapes.

Overall, the topic of circles and quadrilaterals in Class 6 ICSE Mathematics lays the foundation for more advanced geometry concepts in higher classes.