There are multiple artists with this name:

1) Omission is a thrash metal band from Spain.

Official Myspace

2) Omission is a rock / hardcore band from The Netherlands.

Official Myspace

3) Omission was a thrash metal band from the United Kingdom. They released one EP entitled "Black Box Recordings" in 2005.

Band Info

4) omission is a slowcore /alternative rock artist from the United States. Read more on Last.fm. User-contributed text is available under the Creative Commons By-SA License; additional terms may apply.