Burst is an overloaded word. We use it in both GPIF and USB.
In USB, a packet is just a chunk of data/information that is sent as a single unit. It can contain data you send/receive or it can contain house-keeping information that the bus uses.
A burst (in USB) is just a collection of packets that are sent before an acknowledgement is received from the receiver. For example, if the PC is reading data from an IN endpoint, then the packet sequence will look like this: t = 0 ACK TP (NumP = 4): t = 1 DP... t = 2 DP... t = 3 DP... t = 4 DP...
This 4 packet collection is a burst. You can read the USB spec for more information.
GPIF bursts are different and are as you described.