Muslims fast during Ramadan which is 30 days period every year. They fast from every sunrise to every sunset for 30 days. During this time they cant eat or drink. They cant even brush smoke cigarette or somesay they cant even brush their teeth as its a common belief that nothing should get in to your mouth. Traditionally should not cuss nor talk bad about others also.
The purpose of it is that so they can clean their body and their mind. They can feel what hungry people feel. They can live how poor people live. They can get close to God and pray more during this time of year.