When brain cells (called neurons) send signals to one another, they release a little bit of a neurotransmitter so that the message can be delivered. They then have to take back the neurotransmitter they released so they can send the next message. This process of replacing the neurotransmitter is called “reuptake.”
SSRI's or Selective Serotonin Reuptake Inhibitors, are a class of antidepressant medications that are used to treat major depressive disorders. They block the reuptake of serotonin in the synaptic cleft thus increasing the concentration of serotonin.