You can check this article on Quixel website which gives an extensive definition for each material channel.
And from my experience :
Color : diffuse / color / base color / albedo ( the last one is not correct but whatever )
AO : in the collor channel, blend it on top of the color map in Product mode.
Reflection : reflection / specular ( meant to be load in the reflection channel, don't use it )
Metal : metal / metallic ( load it in the corresponding slot )
Glossiness : glossiness / roughness ( in the corresponding slot )
Normal : normal / normalbump ( in the corresponding slot, check if your render engine follow the DirectX or OpenGL reference)
Bump : bump / detail ( in the corresponding slot )
Displacement : height / displacement ( in the corresponding slot )
All maps are meant to be used in linear space ( color profile : linear or gamma 1.0 ) except Color, AO, Translucency Color.
Hope it helps,