a	b	c	d	e	f
1	a1	b1	c1	d1	e1	f1
2	a2	b2	c2	d2	e2	f2
3	a3	b3	c3	d3	e3	f3
4	a4	b4	c4	d4	e4	f4
5	a5	b5	c5	d5	e5	f5
6	a6	b6	c6	d6	e6	f6

An alphanumeric grid (also known as atlas grid) is a simple coordinate system

Coordinate system

In geometry, a coordinate system is a system which uses one or more numbers, or coordinates, to uniquely determine the position of a point or other geometric element. The order of the coordinates is significant and they are sometimes identified by their position in an ordered tuple and sometimes by...

 on a grid

Grid (spatial index)

In the context of a spatial index, a grid is a regular tessellation of a manifold or 2-D surface that divides it into a series of contiguous cells, which can then be assigned unique identifiers and used for spatial indexing purposes...

 in which each cell is identified by a combination of a letter and a number.

An advantage over numeric coordinates, which use two numbers instead of a number and a letter to refer to a grid cell, is that there can be no confusion over which coordinate refers to which direction.

Algebraic chess notation

Algebraic chess notation

Algebraic notation is a method for recording and describing the moves in a game of chess. It is now standard among all chess organizations and most books, magazines, and newspapers...

 uses an alphanumeric grid to refer to the squares of a chessboard

Chessboard

A chessboard is the type of checkerboard used in the board game chess, and consists of 64 squares arranged in two alternating colors...

.