A Concentrate is a high potency CBD extract, exceeding 70% CBD and up to 99.9% depending on the exact type.
CBD oil is a concentrate diluted in a carrier oil. Hence it features a lower percentage of CBD. CBD extracts when consumed on their own, without dilution offer stronger effects than those typically felt by using CBD oil.
Also, CBD concentrates are often consumed via a CBD vape pen or dab rig (or pen) and as a result, are felt quicker as the CBD enters the bloodstream much faster when vaping than when using CBD drops.