Originally Posted by SSIndyRider

Intervals normally refers to training sessions that involve a specified time of hard riding, then a specified recovery time riding slower and alternating them - e.g. warm up, hard, recovery, hard, recovery, cool down. The timing of each depends on goals desired and there are plenty of combinations.

Spinning is normally a couple of possibilities - indoor stationary cycling; typically setting an RPM rate, like 90-100 RPMs as a maintained speed. The other is "spinning up a hill" - gearing so that you maintain a faster RPM Cadence by down-shifting, rather than a hard slow cadence in a higher gear (mashing).

At least, that's how I understand those two terms, but I'm relatively new around these parts...