A wiki is a website where users can add, remove and edit every page using a web browser. Access is flexible – all that is needed is a computer with a browser and Internet connection.  Wikis interrelate people together. If one wants to tell his/her friends something, he/she can sign up in wikispaces.com write his idea and everybody can see it editing answers to the written idea. Wikis also motivate students to learn. It has some advantages and disadvantages .
Advantages
1. They provide collaborative learning environment and promote communication skills in some aspects. Wikis  help learners develop social skills. Students are encouraged to being authors and develop communication skills, especially in writing and reading, while class activities take place in virtual setting rather than traditional classroom.   
  2.They offer an easy publishing tool for posting information as well as getting feedback to and from public. Both of them are easy to learn and use with pre-designed templates and step by step user guidelines. 
3. Enable educators and learners to expand the learning circle with parents, communities, or even the people around the world who has access to the Internet. They allow users by sharing their articles, views and comments to build a network with similar interests.
Disadvantages
1.  Users can be distracted easily. Once the students get connected with wikis, they also have access to the entire virtual world and can get diverted away from their tasks easily. 
2.Plagiarism and copyright issues. The publishers need extra caution not only to make sure all the postings are original or the quotations from others are clearly remarked, but also for prevention from outsiders stealing their intellectual properties. 
3.   Hard to grade and assess. It can be overwhelming for educators to grade either too many or too few entries are posted by students.
As for me wikis can really be of great help for students, for their learning process and sharing ideas. Wikis can develop students writing and reading skills. It is useful for them to read each students comments and find something new about the same topic.