Seva (pronounced say-va) is a Sanskrit word yet there is no word in English that really defines seva. Service itself is not seva. Seva is serving and helping others with compassion, serving not for personal gratification but to uplift others. Seva is not meeting your own aims, but offering that service as a homa, as an offering in the yajna of life.
Seva contains the best there is in you. When it is offered to another being and it contains your best thoughts and feelings, your love and affection, sympathy and compassion, then that action becomes a blessing in disguise to uplift another being.
With the desire to uplift and assist people, giving help and compassion to others with no thought of what is to gain or what is to be lost by doing so it becomes a miraclous gift and the on the path to self-realization, which is the essence of yoga.
Practice seva. Give back to others without the expectation of any reward or acknowledgment.