1. Information that is essential to understanding a situation or problem
   - background

Type of: information

• activation energy
• activator
• active
• active agent
• active air defense
• active application
• active birth
• active citizen
• active immunity
• active matrix screen
• active placebo
• active site
• active transport
• active trust
• active voice
• actively
• activeness
• activewear
• activism
• activist
• activistic
• activity
• actomyosin
• actor
• actor's agent