Coarse Acquisition (C/A) refers to a code used by GPS satellites to transmit signals to GPS receivers. The C/A code is a pseudorandom noise (PRN) code that is used for initial acquisition and coarse positioning of the receiver. It is a relatively simple and robust code that allows receivers to quickly acquire the GPS signal and determine their approximate location.

The C/A code is transmitted on the L1 frequency (1575.42 MHz) and is available to all GPS users. It has a chipping rate of 1.023 Mbps and a period of 1 millisecond, which means it repeats every 1 millisecond. The C/A code is used in conjunction with the P-code (Precise code) to provide accurate positioning and timing information.

The C/A code is "coarse" because it provides an accuracy of around 100-200 meters, which is not as precise as the P-code. However, the C/A code is still widely used because it is simple to implement and provides a reliable means of acquiring the GPS signal.