Let's go with "delta transfer algorithm" (thanks, Matt).

rsync.yo

@@ -964,7 +964,7 @@ correctly and ends up corrupting the files.
 dit(bf(-n, --dry-run)) This tells rsync to not do any file transfers,
 instead it will just report the actions it would have taken.
 
-dit(bf(-W, --whole-file)) With this option the differential rsync algorithm
+dit(bf(-W, --whole-file)) With this option the delta transfer algorithm
 is not used and the whole file is sent as-is instead.  The transfer may be
 faster if this option is used when the bandwidth between the source and
 destination machines is higher than the bandwidth to disk (especially when the
@@ -1706,7 +1706,7 @@ after it has served its purpose.
 Note that if bf(--whole-file) is specified (or implied), any partial-dir
 file that is found for a file that is being updated will simply be removed
 (since
-rsync is sending files without using the differential rsync algorithm).
+rsync is sending files without using the delta transfer algorithm).
 
 Rsync will create the em(DIR) if it is missing (just the last dir -- not
 the whole path).  This makes it easy to use a relative path (such as
@@ -1824,7 +1824,7 @@ sender's file, which is being reconstructed at a rate of 110.64 kilobytes
 per second, and the transfer will finish in 4 seconds if the current rate
 is maintained until the end.
 
-These statistics can be misleading if the differential transfer algorithm is
+These statistics can be misleading if the delta transfer algorithm is
 in use.  For example, if the sender's file consists of the basis file
 followed by additional data, the reported rate will probably drop
 dramatically when the receiver gets to the literal data, and the transfer