Asherah is the name used in the Bible for either a pagan goddess or a particular type of cultic image (the tree/pole). There is some debate as to whether the term applies to both examples. According to the English Standard Version, Asherah is referred to 21 times, primarily in 1 and 2 Kings.
As a goddess
Asherah was a Syrian goddess, the consort of one of the Baals, and based in Lebanon. According to texts from Ugarit she was the consort of El, and the mother of seventy other gods. Thus, she was a fertility goddess. Passages such as 1 Kings 18:19 reflect this idea:
Jeremiah refers to Asherah as the Queen of Heaven and denounces worship of her; she is also known as Astarte.
Now summon the people from all over Israel to meet me on Mount Carmel. And bring the four hundred and fifty prophets of Baal and the four hundred prophets of Asherah, who eat at Jezebel's table. (NIV)
As a cultic image
Asherah was also understood as an idolatrous symbol that was used by the Israelites in turning away from God and worshipping the gods of surrounding nations. One example is in 1 Kings 15:13, in which:
He [Asa] even deposed his grandmother Maacah from her position as queen mother, because she had made a repulsive Asherah pole. Asa cut the pole down and burned it in the Kidron Valley. (NIV)