Definition:Order


 * Abstract Algebra: Order of an Algebraic Structure.


 * Matrix Algebra: Order of a Square Matrix.


 * Group Theory: Order of an Element in a Group.


 * Number Theory: Order of an Integer: the least positive integer $$c$$ such that $$a^c \equiv 1 \pmod n$$.


 * Analysis: Order of a Polynomial (otherwise known as its degree).


 * Calculus: Order of a Derivative: the number of times a function has been differentiated.


 * Differential Equations: Order of a Differential Equation: the highest order derivative that appears in that differential equation.


 * Graph Theory: Order of a Graph: the number of vertices in a graph.


 * Set Theory: Ordering.