what does "timespan?" mean in c#?

what does the question mark mean at the end of the variable?

TimeSpan? begin = // bla bla bla

The c开发者_如何学运维oding language is c#

This is Nullable type. It means that value of begin can be null or a timespan

TimeSpan? and Nullable<Timespan> is same thing

TimeSpan? means you're declaring a nullable type. A type which can support null values.