Define homeostasis?

Homeostasis is the condition when a system or an organism tries to maintain itself within a narrowly defined ‘zone of comfort’
All living organisms need ideal or near ideal conditions to survive. Essential processes such as blood pressure, pH, partial pressure of oxygen in the blood, body temperature etc. have to be maintained at or near desired values for survival, growth and reproduction.
The processes by which organisms try to maintain these conditions are known as homeostasis.
Chemical reactions, whether within living organisms or in vitro, are governed by concentration of reactants, temperature, pressure etc., so as to reach equilibria in which the concentrations of reactants and products are maintained at constant values. That too is homeostasis.