Definition:
With regards to a specific relationship, a connection that requires a higher than average amount of time or energy investment.
With regards to a person within a relationship, high maintenance can refer to several things: having higher than normal expectations of a person in a relationship, the requirement one has for high amounts of affection and reassurance within relationship, or being unusually intense in a relationship with regards to needs and/or demands and therefore being difficult or challenging.
Examples:
You might not want to date her; she's high maintenance.
