A lot of people–especially new Muslims–break their heads on this conundrum. What is the difference between fard and wajib? Are they the same? Are they different? What’s the scoop? Why do some people say fard, while others say wajib for the same things?
The answer is simple. According to the majority of scholars, fard and wajib mean the EXACT same thing. There is no difference. They are interchangable. (Recall that fard means: an action that, if performed, entails reward, and if neglected, entails punishment.)
However–there is one exception. The Hanafi madhab differentiates between the two. They say that denying a fard makes you kafir, while denying a wajib does not. Note that here, we’re talking about denying an action, not neglecting it–so if someone says, “no, I don’t have to pray, prayer is not obligatory,” that’s denying a fard, while someone else who says “yes, prayer is obligatory but I don’t feel like praying,” is sinning (major sin).
In the end, it’s like saying “forest” or “trees”–some say fard, and some say wajib, but they’re the same thing.
And Allah, Al-Aleem, knows best. We ask Allah to increase us in knowledge that will benefit us and protect us from knowledge that has no benefit, ameen ya rabbi!