From main + stream.

mainstream

1. Used or accepted broadly rather than by small portions of population, market, scientific community, etc.

   They often carry stories you won't find in the mainstream media.

• (used or accepted broadly) common, usual, widespread, conventional

• fringe, nonmainstream, alternative

• French: commercial, conventionnel
• German: Mainstream, etabliert, konventionell
• Italian: virale, corrente, comune, convenzionale, conformista, prestabilito, tradizionale, flusso mediatico predominante
• Portuguese: convencional
• Russian: мейнстри́мовый
• Spanish: normal, aceptado, tipico, cotidiano, convencional

mainstream (plural mainstreams)

1. The principal current in a flow, such as a river or flow of air
2. (usually, with the) That which is common; the norm.

   ideas outside of the mainstream

• German: Hauptrichtung, Mainstream
• Russian: основное направление
• Spanish: común y corriente

mainstream (mainstreams, present participle mainstreaming; simple past and past participle mainstreamed)

1. (transitive) To popularize, to normalize, to render mainstream.
   • 2011, Jeff Change, Can't Stop Won't Stop: A History of the Hip-Hop Generation, page 420:

     Just as the gang peace movement desired to mainstream hardcore bangers into civic society, The Chronic wanted to drive hardcore rap into the popstream.

2. (intransitive) To become mainstream.
3. (transitive, education, chiefly, US) To educate (a disabled student) together with non-disabled students.