I have my RAM configured dual channel but what is single/dual rank and how to find which it is?

A memory rank is a block or area of data that is created using some, or all, of the memory chips on a module. A rank is a data block that is 64 bits wide. On systems that support Error Correction Code (ECC) an additional 8 bits are added, which makes the data block 72 bits wide. Depending on how a memory module is engineered, it may have one, two, or four blocks of 64-bit wide data areas (or 72-bit wide in the case of ECC modules.) This is referred to as single-rank, dual-rank, and quad-rank.