Dropped domains are the domains which are deleted. So these are terminated, delted or are automatically expired at the provider. So it may be that the domains were deleted unintentionally.Usually you speak about deleted domains, not about dropped-domains.
Expired domains are also called liberated domains. However, mostly we speak of RGP-domains (Redemption-Grace-Period).
Exactly this are the domains you can auction at nicsell. Our auctions are always running 14 days. So you have to start 14 days before a RGP-domain gets free again. If you win the auction, we will try to catch the domain for you.
dropping: "to drop down something"
When a domain is dropped, it is delted and terminated at the provider. This domains are then called drop-domains.
Domains are billed monthly at the provider, so that they could be deleted at the end of the month. The principle is, who owns the domain on the 1st of the month have to pay for it too. Therefore, most domains are deleted 30th of a month. Partially the domains could be cancelled immediately.
The term dropping is actually used less often, rather is said delete or cancel. Instead of dropped domains you also use more often expired domains or RGP domains.