What are the differences between composer update and composer install?

Here are few key differences:

Point of Difference	Composer Update	Composer Install
Update and Install latest Dependencies	Yes. It read composer.json. Check for latest version of the package and install it.	No. Install all dependencies specified in composer.lock file
What if no composer.lock file	Create it	run composer-update and create it
Update composer.lock?	Yes	No
When to use?	Development Phase	Deploying Phase