A slow-and-steady appreciation of financial market prices over time. A tortoise rally contrasts with more volatile rallies where prices rise and fall quickly while maintaining a general upward trend.
Taobiz explains Tortoise Rally
Long-term retail investors generally enjoy the steady gains produced by a tortoise rally. However, active traders and hedge funds can become frustrated by the lack of quick drops and rises that allow these players to capitalize on their superior information and market access. For them, volatility creates opportunities to buy underpriced securities for the long haul or to create short-term trading profits.