By default, all accounts on Deribit use a segregated standard margin (S:SM) system. With this margin system, the entire balance of a particular asset will be used as margin for positions in that asset, and each position shares that same pool of margin with each other. Note that this margin sharing does not apply to long option positions unless portfolio margin is enabled. Also note that the sharing of the same pool of margin in the standard margin system does not imply any offsetting of margin requirements. For offsetting margin requirements (e.g. a long call vs a short call), portfolio margin must be enabled.
As an example of how the shared margin works, imagine an account with one long future and one short future in the same asset but with a different expiry date. Profits on one position can offset losses on the other automatically, without the need to manage how much margin is assigned to each position separately. As long as the margin balance of the account remains higher than the combined maintenance margin requirements, the positions can remain open.
Some other platforms have a system called isolated margin. An isolated margin system would set aside a specific amount of margin that is only to be used for a single position. This position and the margin used for it would be isolated from the rest of the account and any other positions. On Deribit, the only way to assign a specific amount of margin to a specific position is to isolate that margin and position in its own subaccount.
For traders who prefer to isolate positions, or even groups of positions, and assign specific portions of their capital to them, Deribit provides traders with the ability to create multiple subaccounts within the same master account.