Middle-term memory, also known as intermediate-term memory, is a stage of memory that exists in between short term/working memory and long-term memory. As working memory and short-term memory last from a few seconds to approximately 30 minutes and long-term memory lasts from 30 minutes to a lifetime, middle-term memory has an overlapping effect between these two other types of memory. It exists beyond the short-term memory frame and can continue into long-term memory.
For example, the memory of school tasks often fall into this category. Most of us learned mathematical rules in algebra along with grammar and punctuation rules in early schooling and remembered them at least as long as you were being tested on it. But now, as adults, our memories of these subjects often have faded.