A **TTY** (i.e. **T**ele**TY**pewriter) is a special device that lets people who are deaf, hard of hearing, or speech-impaired use the telephone to communicate, by allowing them to type text messages. A TTY is required at both ends of the conversation in order to communicate. 
OR 
**TTY** is **terminal** which is used to type text message.
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**Shell** :the outside protective covering part of a seed i.e. kernel. 
OR 
framework or exterior structure to central or essential part of a system. 
[![enter image description here][1]][1]
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**Console** means the keyboard and monitor physically attachements to a computer.


 [1]: https://i.sstatic.net/muYsK.jpg