How to make a popup like in the image when we click a link and what it is known as?

Sign Up to our social questions and Answers Engine to ask questions, answer people’s questions, and connect with other people.
Login to our social questions & Answers Engine to ask questions answer people’s questions & connect with other people.
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Please briefly explain why you feel this question should be reported.
Please briefly explain why you feel this answer should be reported.
Please briefly explain why you feel this user should be reported.
I believe you can achieve that if you use a PopUpWindow and set the backgound to be bubble like that in the picture you are showing in your question. See the answer of this previous SO post for a simple example.