Step 1: State the meaning directly:
Non-cooperation meant a deliberate, organised withdrawal of Indian cooperation from every British institution -- schools, courts, councils, goods, titles -- as a non-violent weapon of protest.
Step 2: Explain the immediate trigger:
Public outrage over the Rowlatt Act and the Jallianwala Bagh massacre gave the movement its immediate emotional and political trigger.
Step 3: Explain the strategic reasoning:
Gandhi saw it as a way to unite Hindus and Muslims (via the Khilafat cause) and to build mass, disciplined political pressure toward Swaraj without resorting to violence.
Step 4: Note its conclusion:
It ended in 1922 after the Chauri Chaura violence broke its non-violent character.
Final Answer:
\[ \boxed{\text{A non-violent boycott movement, launched over the Rowlatt Act/Jallianwala Bagh and the Khilafat issue, to achieve Swaraj}} \]