This term just occurred to me and I didn't see it in wide usage already so here goes...
I'm working on an application that needs to present a graph of stock prices over a given time for a list of securities. The data is missing in some cases, for example weekends, and the graph should not be discontinuous. If however the start date is Saturday there is no previous day's data in the dataset so it has to use the day (or two, or three, ...) ahead's. From the point where data appears we baxtrapolate the data to the start point.
Related: baxtrapolation (n.)