The term in context is used to note that the music can only be used in context, i.e. only in the way it was originally synched with the images. For film this means that an in-context use only refers to that specific scene in that specific timing and excludes a use in a different timing to the images (e.g. as an underlying music of the collage used in a trailer –> see Out Of Context).
In simple words this means forever. It refers to a never ending license term.