Tolerance relating to drug abuse is the phenomenon where a drug user's body develops an "immunity" to the effects of the drug.  In essence, as a drug user continues to use a drug it takes more and more of that drug to get the desired effect, or high.

Withdrawal refers to the physical and psychological effects that result from discontinuing the use of a drug.  The severity of the withdrawal can vary based on the user and the drug in question.  Typically, the withdrawal correlates with the strength of the drug and the time period the drug was abused.  The stronger a drug is and the longer it is used will cause more severe withdrawal symptoms.

Drug dependence is a condition where a person can no longer physically function without the use of the drug they are using.  It is usually linked to non-addicting drugs like prescription medications.