g’s

You should have given more detail about it, where you have encountered.

The notation "g" is for acceleration due to gravity on Earth and is equal to approx. 9.8 m/s2. So, any acceleration can be expressed in the unit "g". For example acceleration of value 98 m/s2 can also be expressed as 10 g's. But it is normally used to compare the acceleration due to gravity on other heavenly bodies like Moon or Jupiter to compare with that of Earth. It is much similar to expressing the distance of planets from Sun in Astronomical Units (AU) which is nothing but average distance of Earth from Sun.

Taken from:Units: G

g

a symbol for the average acceleration produced by gravity at the Earth's surface (sea level). The actual acceleration of gravity varies from place to place, depending on latitude, altitude, and local geology. The symbol g is often used informally as a unit of acceleration. By agreement among physicists, the standard acceleration of gravity g_n is defined to be exactly 9.806 65 meters per second per second (m/s²), or about 32.174 05 feet per second per second. At latitude p, a conventional value of the acceleration of gravity at sea level is given by the International Gravity Formula,
g(p)=9.7803267714(1+0.00193185138639sin²(p))/√(1-0.0069437999013sin²(p)). The variation, caused by the oblateness of the Earth and the accleration we experience due to the rotation of the Earth, is about half a percent, from 9.780 327 m/s² at the Equator to 9.833 421 m/s² at the poles. The symbol g was used as a unit first in aeronautical and space engineering, where it is important to limit the accelerations experienced by the crew members of aircraft and spaceships: the "g forces," as they are called. This use became familiar through the space programs, and now a variety of accelerations are measured in g's. The names gee and grav is also used for this unit. Note that g is also the symbol for the gram.

GA.