Often times in our Industry we see the occurrence of the word Manual Tester/Testing and Functional Tester/Testing. On many occasions, I have seen the former being used in place of the latter and vice versa. 
The majority of credit for creating confusion and amalgamation of these two different terms into goes to Job postings/listings. Also, to some schools of Testing who teach and preach Manual Testing as a concept.

Manual Testing is a term that fits in the manufacturing industry, where a person would have to go and put effort into using muscles and testing something. 
Example: Consider the automobile industry, where they build automobiles. If they test the components physically by applying their muscle and manpower, it would be termed Manual Testing (Usually done at the prototype stage). Similarly, when production is at a large scale, the testing is done by machines, which qualifies as Automation Testing. Manual or Automation testing in Software could be a topic/discussion for another Blogpost.

Now lets look at the IT industry where we build software. What do we mean by Manual testing of Software? We aren’t flexing any muscular energy(using hands, or legs) to test it. How relevant is the term Manual Testing in our context?
Okay, now you may say that we write test cases, and execute test cases as part of a manual effort. But so does Automation Testing, where they build automation scripts. So, writing test cases and then testing the software would qualify as Scripted Testing, and not Manual Testing. 

Manual Testing is not a term that fits our industry, we do more of brainual testing. 

To understand why we test, check out this blogpost

Now coming to Functional Testing, I see a lot of Testers addressing themselves as Functional Testers but they restrict themselves only to testing functional components of UI and UX. Is that it? No, there is a lot to functional Testing than just the UI elements. Listed down below are some Functional Testing Heuristics that we can incorporate in our Testing. 

Source: Testing References, Joris Meerts

I hope this clears the air and I could put some light on these frequently misinterpreted terms.

Thanks for reading and do let me know if you had similar encounters with these words.