Sequence is an ordered set whose elements are usually determined based on some function of the counting numbers, e.g. a geometric sequence is a set where each element is a multiple of the previous element; an arithmetic sequence is a set where each element is the previous element plus or minus a number.

Set is a collection of distinct objects or numbers, without regard to their order, considered as an object in its own right. 

Slope is the steepness or incline of a line, determined by reference to two points on the line, e.g. The slope of the line y = mx + b is m, and represents the rate at which y is changing per unit of change in x.

Subset is a subsidiary collection of objects that all belong to, or is contained in, an original given set, e.g. subsets of {a, b} could include - {a}, {b}, {a, b} and {}. 

Symmetry is the correspondence in size, form or arrangement of parts on a plane or line (line symmetry is where each point on one side of a line has a corresponding point on the opposite side, e.g. a picture a butterfly with wings that are identical on either side; plane symmetry refers to similar figures being repeated at different but regular locations on the plane).