noun

• (military) Military unit composed of several regiments (or battalions) and including soldiers from different arms of service.
• (derogatory) A group of people who share views or a specific characteristic.
  "More sympathy for career criminals from the bleeding-heart brigade!"
• (Internet slang) Coordinated online harassment, disruption or influencing, especially organized by an antagonistic website or community.
  "We've definitely seen an increase in abusive content since certain areas began COVID lockdowns and stay home orders, we suspect because of the growth of people having time to waste doing these sorts of brigades."

verb

• (Internet slang) To harass an individual or community online in a coordinated manner.