What is the difference between a destroyer and a destroyer escort?

I served in the Australian Navy in the 1960s and early 70s. Destroyers became bigger ships after WW11. When I 1st joined HMAS Derwent, she was a Type 12 frigate. After we got our American built Charles F. Adams destroyers, our type 12 frigates were re-designated as destroyer escorts. The Type 12s,or Whitby class to give them their original name, were around 2,500 tons. Bigger than a lot of WW11 destroyers. The Charles F.Adams Class were over 5000 tons. In WW11 and prior to that they would have ben designated as cruisers. I believe the different names simply indicate larger and smaller destroyers. Allen Lyne ex-POUC, RAN