Concurrent training is typically defined as the performance of strength and endurance training within the same session:

The interference effect is phenomenon whereby the performance of endurance training in the same session to strength training may attenuate strength, power and hypertrophy gains.

Non-concurrent training is the performance of strength and endurance training on separate occasions (not in the same session)

Evidence show that concurrently training muscular strength and cardiovascular endurance has no benefit to running economy

According to Wilson et al. (2012) the interference effect of endurance exercise on strength adaptation is most likely observed when running (compared to cycling) is the endurance activity.