A SEGY file is a data file saved in the SEG-Y format, which was developed by the Society of Exploration Geophysicists. It contains geophysical data, such as the coordinates of reflected seismic waves, surface elevation, and water depth. SEGY files also store metadata, which includes the date and time of the data acquisition, projection zone and method, type of instrument used to acquire the data, and the sweep frequency and length.

SEGY files are used to map and measure the properties of the subsurface of the earth. The files store data recorded by various seismology instruments that are used to send a controlled energy to the subsurface and record reflected waves, much like sonar devices. SEGY files can be opened and viewed using various programs, such as Geopsy, Seismic SEGY Toolkit, and kogeo. The SEGY format evolved from the SEG format, which was originally published in 1975 and is widely used in the geophysical industry. Because of its extensive use, the format has evolved over the years, with more capabilities added in subsequent revisions and variations. NOTE: SEGY files may also be saved as .SGY files.