What is the difference between Speculative Inventory and Pipeline inventory?

Speculative Inventory is  inventory used to serve a predicable rise in demand and is held for short periods on an irregular basis to take advantage of an imminent  rise in demand e.g. during  festivals.

Pipeline Inventory is the inventory in transit.The time of transit can be reduced leveraging several factors incl faster transport,vicinity location etc.

Pipeline inventory is the actual inventory either in transit, with the vendor or present in the system in the form of Open PO.

Speculative inventory is a broader term which already includes pipeline inventory and even the inventories that you are going to raise in the near future.

Usually speculative inventory is used for a longer horizon whereas pipeline inventory is for any given moment.