The word "stimulant" can refer to any type of drug that increases activity in the central nervous system or sympathetic nervous system, ranging from caffine to methamphetamine.
The most common recreational
stimulants are commonly called "
uppers" and include ADHD medications (
adderall,
ritalin, etc), amphetamines, cocaine, and ecstacy.
The more addictive stimulants generally give the user a sense of euphoria that might include alertness, possible twitching and an overall sense of well-being.
Nicotine, the addictive subtance in tobacco, is a well known stimulant but can also be sedating in higher doses.