What is the difference between mega cap and large-cap?

Could you elaborate on the key distinctions between mega-cap and large-cap companies in the financial market? I understand that both represent significant market capitalization, but I'm curious about the nuances that set them apart. In particular, I'm interested in knowing how these classifications affect investment strategies, risk profiles, and potential returns. Additionally, I'd like to know if there are any industry-specific trends or patterns that tend to characterize mega-cap versus large-cap firms. Clarifying these differences would help me better navigate the investment landscape and make informed decisions regarding my portfolio allocation.