Any one of many species of Old World singing birds belonging to Motacilla and several allied genera of the family Motacillidæ. They have the habit of constantly jerking their long tails up and down, whence the name.

Old World bird having a very long tail that jerks up and down as it walks

The Motacilla wagtails are a genus of small passerine birds with long tails which they wag frequently. Motacilla, the root of the family and genus name, means moving tail. The Forest Wagtail belongs to the monotypic genus Dendronanthus which is closely related to Motacilla and sometimes included herein.

Wagtail is a client/server-based tool for audio encoding. It is designed to make it easier to encode and organize files in bulk. Wagtail allows you to enforce standards across your media collection with the use of "formats", each describing an audio format, how to encode/tag, etc.