Modes

The PSK Automatic Propagation Reporter automatically gathers reception records of PSK activity.

Radio waves have three characteristics that can be changed, Amplitude, Frequency and Phase. A mode is the way of changing electromagnetic waves.

By modulating waves, transmission of information is possible.

From amateur-radio-wiki.net there's a very brief but complete description of:

WSPR (pronounced "whisper") stands for "Weak Signal Propagation Reporter".

WSPR implements a protocol designed for probing potential propagation paths with low-power transmissions. Transmissions carry a station's callsign, grid locator, and transmitter power in dBm. The program can decode signals with S/N as low as -28 dB in a 2500 Hz bandwidth.
The WSPR protocol compresses the information in the message into 50 binary digits.

WSPR characteristics: