2. Interval censoring is when a value is only known to lie within some interval. The most common example would be when data have been rounded. Thus, for example, a value of 5 implies the original value was in the interval $[4.5,~5.5)$. In a survival analysis context, it may only be known that a patient's symptoms reemerged between their 2nd and 3rd checkups.
3. Left censoring is when a value is only known to be less than some amount. An example might be when the reemergence of symptoms is discovered in the 1st checkup. Note that since durations cannot be $<0$, left censoring can often be considered a special case of interval censoring.