Aerin was a woman closely related to Húrin Thalion.
She secretly helped Húrin's wife Morwen. When Túrin, son of Húrin, returned to Dor-lómin, he learned from Aerin that his mother had left Hithlum, and in his rage he killed Brodda, thereby also sealing Aerin's fate, who burnt herself alive in her halls, and the remainder of the House of Hador now was persecuted even more cruelly.
The name incorporates aer "ocean". The ending perhaps is the same in the names of Húrin and Túrin; in that case the name would mean "She who desires the Sea".