Midrash is a form of rabbinic literature. There are two types of midrash: midrash aggada and midrash halakha.
Midrash aggada can best be described as a form of storytelling that explores ethics and values in biblical texts. ("Aggada" literally means "story" or "telling" in Hebrew.) It can take any biblical word or verse and interpret it to answer a question or explain something in the text. For instance, a midrash may attempt to explain why Adam didn’t stop Eve from eating the forbidden fruit in the Garden of Eden. One of the best-known midrashim (plural of midrash) deals with Abraham’s childhood in early Mesopotamia, where he is said to have smashed the idols in his father’s shop because even at that age he knew there was only One God. Midrash aggadah can be found in both Talmuds, in midrashic collections and in Midrash Rabbah, which means "Great Midrash."
Whereas midrash aggada focuses on biblical characters as they pertain to values and ideas, midrash halakha focuses on Jewish law and practice. Midrash halakha attempts to take biblical texts that are either general or unclear and to clarify what they mean. A midrash of this nature may explain why, for instance, tefillin are used during prayer and how they should be worn.