What are the different types of memory T cells?

Memory T cells are long-lived T cells that remain after exposure to an antigen and mediate a more rapid and more potent response upon re-exposure to the same antigen. 

There are 5 types of memory T cells.

1. Central memory T cells (TCM)  
2. Effector memory T cells (TEM)
3. Tissue-resident memory T cells (TRM)
4. Stem cell-like memory T cells (TSCM)
5. Virtual memory T cells (TVM)