This is a clip from the Dynamics GP Help on Valuation methods and defines the difference between the 4 very similarly named types.
If you still have questions, please feel free to post. But might I suggest you open a current help session - old threads get less looks than current ones ( just me )
Valuation methods determine how the costs of inventory items are calculated. While you can have different valuation methods for different items or companies, we recommend that you talk to your tax accountant before changing the valuation method you currently use. The following table describes the valuation methods available and explains how each is used.
Valuation method
FIFO perpetual
Items purchased first are considered sold first (First In, First Out). Detailed information about the cost of all items is maintained, and the inventory is valued at its actual cost. The current cost for items is the cost of the item the last time it was purchased.
LIFO perpetual
Items purchased last are considered sold first (Last In, First Out). Detailed information about the cost of all items is maintained, and the inventory is valued at its actual cost. The current cost for items is the cost of the item the last time it was received.
Moving average perpetual
The cost of items with the same item number is totaled and an average cost is assigned to the items. The average cost of an item is revalued throughout the period as you enter increase transactions for items. The average cost also is used as the current cost. The formula is:
(Current units x current moving average cost) + (New units x purchase price) / (Current units + new units)
FIFO periodic
Items purchased first are considered sold first (First In, First Out), and are valued at their standard cost. To update the standard cost, you can use the Inventory Year-End Closing window. At the end of the year, the standard cost can be adjusted to the current cost.
LIFO periodic
Items purchased last are considered sold first (Last In, First Out), and are valued at their standard cost. To update the standard cost, you can use the Inventory Year-End Closing window. At the end of the year, the fixed cost can be adjusted to the current cost, or the cost of the item the last time it was received.
Cost variances—which can result with any of the valuation methods—are tracked in the General Ledger using the Inventory Variance account.