COPY words_reviews (uid, author, nice, review, updated) FROM stdin WITH (FORMAT csv); 1,2,1,'1 is nice by 2','2017-03-01' 1,3,1,'1 is nice by 3','2017-03-02' 1,4,1,'1 is nice by 4','2017-03-03' 2,1,1,'2 is nice by 1','2017-03-01' 2,3,1,'2 is nice by 3','2017-03-02' 2,4,0,'2 is not nice by 4','2017-03-03' \.
but I am confused about the comments that I should use \copy and not just COPY and also that I could leave out WITH and brackets.
The difference between COPY and \copy is explained here:
Basically COPY runs as the server user and so the files it uses have to be accessible by the user the server runs as. \copy is a psql meta command that runs as local user so it can access files the local user can see and has privileges on.
I take it, then, if one chooses not to use pre-existing files and instead inline the content as shown here, the choice between \copy and COPY becomes a matter of style and not correctness. As a matter of style using \copy makes it clear that everything that is needed to make the command work exists locally.
The advantage to using "COPY FROM|TO stdin|stdout" is that the copy command itself could (not tested) be spread out over multiple lines - which especially for COPY TO can be advantageous. The entire \copy meta-command cannot be split up.