Standard Cost is the tax inclusive purchase price of an inventory item. You can set this cost as the default price for purchases, instead of the last purchase price. You can change this cost manually on each purchase.
If you would like one "default" price to be entered on purchases for the item, rather than the last purchase price (which can vary), you can activate a preference that will force this behaviour.
To activate Standard Cost
Go to the Setup menu and choose Preferences.
Click the Inventory tab.
Select the option Use Standard Cost as the Default Price on Purchase Orders and Bills.
If you select the preference:
The Standard Cost (the price entered for the item in the Buying Details tab of the Item Information window) is the price that will appear automatically for the item when you enter a purchase. You can change the price on the purchase, if you want.
If you don't select the preference:
The Last Purchase Price (the price that was recorded for the item the last time you purchased it) will appear automatically for the item the next time you enter a purchase. You can change the price on the purchase, if you want.
What if I select the option to use Standard Cost but no standard cost has been entered against the item?