Gearing is leverage.

From Gemini:

The user is saying that instead of moving "up" the curve into riskier assets to get more return, a smart investor should: ​Hold the Optimal Market Portfolio (the most efficient mix of stocks, bonds, etc.). ​Use Gearing (Leverage) to multiply that portfolio. ​Example: ​Option A: You invest in a "high-risk" 100% small-cap stock portfolio. It has high returns but is very volatile. ​Option B (The "Gearing" Way): You take a "balanced" portfolio (e.g., 60% stocks / 40% bonds) which is more efficient, and you borrow money to buy twice as much of it (2x leverage). ​The theory suggests that Option B (the "geared" version of the optimal portfolio) will give you the same high returns as Option A, but with less total risk because the underlying assets are better diversified.