Sector rotation describes how money moves between industry groups over time. Different sectors do well in different conditions: banks and autos often lead when interest rates fall and the economy grows, IT stocks track the dollar and US spending, FMCG and pharma are seen as defensive when the market is nervous, and metals follow global commodity prices. Large investors shift allocations as their view changes, and the shift shows up in relative performance. Suppose Nifty is flat over a month while Nifty Bank rises 6% and Nifty IT falls 5%; money has rotated into banks. Traders use sector indices and relative strength to find where momentum is, and to avoid buying strong stocks in weak sectors. Rotation is easier to see in hindsight than in real time, and chasing last month's leader often means arriving late.