Laxatives are substances that make you need to defecate. They usually are used by those suffering from constipation. There are different types of laxatives on the market. Most commercial laxatives have either bisacodyl or senna extract as their active ingredient. These laxatives are termed as stimulant laxatives as they stimulate or irritate the lower bowel hopefully allowing defecation. Stimulant laxatives should be used with care and should not be continued for long stretches of time as dependence may occur or health problems might arise.
Other laxatives are things such as Aloe Vera juice/gel or castor oil. These are not normally marketed as laxatives anymore, but carry the same issues as commercial laxatives.
Enemas are also another option, but may be difficult to self administer, messy & again should not be used continually for long periods of time.
Adding dietary fiber to your diet may also help with constipation, reducing the need for laxatives.