What is scientific and technical writing?

Scientific writing is technical writing by a scientist, with an audience of peers -- other scientists.

Scientific writing involves writing lab reports, posters, Biology honors, thesis, scientific journals, research proposals, etc. To become a science writer, you would need a degree/experience in the same field.

On the other hand, technical writing by a technical writer is for novice to intermediate audience about a product/service or concept. Technical writers write user guides (for how to use a software, microwave, machinery), FAQs/Help section that you see on websites, API documents, white papers, requirement specification documents etc. To become a technical writer it is enough if you have a degree in English with an ability to grasp new concepts, research, illustrate and write things in simple Words.