Bulbs are planted in the ground to grow tulips and daffodils.
For implements to theatrical lighting fixtures, see lamp.
Notice in this illustration, "bulb" refers to the outer glass envelope.
As a general rule, a relatively low-wattage "type A" household lamp CAN be called a bulb. Anything else, whether it be for a Fresnel, CYC Light, Ellipsoidal, Par Can, Follow Spot, Moving Light, etc - should ALWAYS be called a lamp. In some parts of the world, "globe," "bubble," and "bottle" (especially with PAR lamps, as in "spin the ___") are also used.