Is it possible to rent an apartment for less than a year?

Yes.  The term of a standard lease is generally 12 months or longer; however, there are multiple methods to rent an apartment for less than one year.  These include short-term leases, sublets and lease breaks.

Short-Term Lease
Any lease with a duration of less than 12 months is considered “short-term.”  Some management companies / landlords offer the option of short-term leases, but may require a minimum term and set a higher asking rent depending on the number of months desired.  These tend to include higher-end luxury doorman buildings, which have corporate and/or furnished apartments as well as increased flexibility to allow for shorter-term leases.

Sublet
Sublets are probably the most common way to rent an apartment for less than a year.  Sublets either involve current rental tenants or condo / co-op owners subletting their apartment (or room, in the case of multiple roommates in a rental unit) for a designated period of time.

For condos / co-ops, there may be specific rules pertaining to a minimum number of months or years for a sublease (sublet), so these situations can vary.  All sublets should involve the execution of a formal sublease agreement to protect both parties.

Lease Break
A lease break occurs when a mgmt co / landlord allows a tenant to terminate a lease prior to the designated expiration date.  Lease breaks are not very common, since many mgmt cos / landlords do not approve such requests.  However, some allow for it, especially with the contingency that the current tenant finds a new tenant who will execute a new lease for the unit.  This minimizes vacancy and limits the risk for the mgmt co / landlord.