As a Noun: 1. A line or surface which is flat and level with the ground or the bottom of a page, rather than at an angle to them; a horizontal line or surface. 2. A raised surface which is flat and level with the ground, rather than at an angle to them; a raised horizontal surface such as a stage or podium. As a Verb or Adjective: 1. To be flat and level with the ground or the bottom of a page, rather than at an angle to them. English = (be) horizontal.