Increasing means getting bigger or expanding. You'll be glad to have an increasing income, but perhaps less glad to have an increasing pants size.
The adjective increasing describes anything that grows or becomes greater. Increasing volume from your neighbor's radio will drive you crazy, since it's getting louder and louder. If your tiny school attracts increasing numbers of new students, it's likely that new teachers will need to be hired. Increasing comes from the verb increase, or grow, with its Latin root word, increscere, "to grow upon, grow over, swell, or grow into."