In reference to earlier comments, yes, "LoD" is "Level of Detail". But, the comments seem to show a misunderstanding. LoDs are a way for games to change model quality for objects depending on how far away from the camera (i.e., how small the object is on screen) the object is. (Look at the "Skeletal Mesh LOD Bias section in this UE4[docs.unrealengine.com] document for an example picture.)

This is what Unity's documentation[docs.unity3d.com] says about Level of Detail and Maximum LOD level:

Level of Detail

Lod Bias - Set the level-of-detail (LOD) bias.
LOD levels are chosen based on the onscreen size of an object. When the size is between two LOD levels, the choice can be biased toward the less detailed or more detailed of the two Models available. This is set as a fraction from 0 to +infinity. When it is set between 0 and 1 it favors less detail. A setting of more than 1 favors greater detail. For example, setting LOD Bias to 2 and having it change at 50% distance, LOD actually only changes on 25%.

Maximum LOD Level - Set the highest LOD that the game uses. See Maximum LOD level for more information.

Maximum LOD level

Unity does not use Models which have a LOD below the MaximumLOD level and omits them from the build (which saves storage and memory space). Unity uses the smallest LOD value from all the MaximumLOD values linked with the Quality settings for the target platform. If an LOD level is included, then Models from that LODGroup are included in the build and always loaded at runtime for that LODGroup, regardless of the Quality setting being used. As an example, if LOD level 0 is used in any Quality setting then all the LOD levels are included in the build and all the referenced Models load at runtime.