Momentum investing is a strategy where investors buy stocks or assets that have shown an upward price trend and sell those with declining prices. The idea is that assets which perform well will continue to do so in the near future. This approach relies on the belief that trends, whether positive or negative, persist for a certain period. It's popular among traders looking for short-term gains, though it carries risks, as market trends can reverse unexpectedly.

Using mutual funds in a momentum investing scanner can help identify funds that are currently trending upwards based on past performance. This strategy allows investors to focus on funds with strong recent returns, though it's important to consider long-term stability and risk.