1. the root of sth, the reason for sth
stems from childhood/training/background
The 'stem' of a plant or flower is the part of the plant leading to the root. When we say something 'stems from' something else we mean it 'comes from' it or is a result of it. You might say that a problem 'stems from' something or talk about where an idea 'stems from'. This more of a formal expression.