Define an orbital.

Orbital is the three-dimensional space around the nucleus in which the probability of finding the electron is maximum. In fact, the orbital is the space around a nucleus in which the probability of finding the electron is almost 95%; only for the rest of time, the electron remains out of it.

It is rather difficult to draw the real picture of an orbital. The best way to represent the orbital is in the form of electron density or electron cloud in terms of small dots. The intensity of dots gives the relative probability of finding the electron in that particular region. It may be noted that the probability of finding an electron is never zero even at a large distance from the nucleus. Therefore, an orbital does not have well-defined boundaries.