Heal over Time (often shortened to HoT) is a term used to describe a beneficial effect given to yourself, your target or/and multiple targets and provides a healing effect in intervals. It is an acronym for the phrase "Health (or Healing/Hit points) over Time" and is a very common MMORPG term. A example of a HoT in Star Trek Online would be the Hazard Emitters ability which restores hull strength for yourself or your target at set intervals over a varying period of time.
HoT effects are typically stronger than direct healing abilities as they take longer to reach their full potential. An example would be the Engineering Team ability (which provides an immediate heal to hull strength for yourself or your target) is always lower in terms of how much it will repair than the Hazard Emitters ability assuming both abilities are of equal rank.
It is very beneficial to use both direct heals and heals over time together to increase healing done although continous direct healing to a target would require more than one player and coordination from your team due to the recharge time and shared cooldowns of abilities.