The first diff explains what happens to a word longer than 'width'. This diff comes from NetBSD and FreeBSD. The explanation is quite complicated and I couldn't understand what this flag does at first, the source code makes it much clearer (the variable is called split_words). But I didn't change the wording, maybe it's just me.
The second diff comes from me, and documents a different way to specify width. The third diff comes from FreeBSD, and makes wording a bit more precise. Index: fold.1 =================================================================== RCS file: /cvs/src/usr.bin/fold/fold.1,v retrieving revision 1.16 diff -u -p -r1.16 fold.1 --- fold.1 28 Dec 2011 22:27:18 -0000 1.16 +++ fold.1 4 Jan 2016 19:13:47 -0000 @@ -57,6 +57,8 @@ in bytes rather than column positions. Fold line after the last blank character within the first .Ar width column positions (or bytes). +If a blank character does not exist within the width, then +a longer line will still be split at the width. .It Fl w Ar width Specifies a line width to use instead of the default 80 characters. .El Index: fold.1 =================================================================== RCS file: /cvs/src/usr.bin/fold/fold.1,v retrieving revision 1.16 diff -u -p -r1.16 fold.1 --- fold.1 28 Dec 2011 22:27:18 -0000 1.16 +++ fold.1 4 Jan 2016 19:12:53 -0000 @@ -39,7 +39,10 @@ .Sh SYNOPSIS .Nm fold .Op Fl bs -.Op Fl w Ar width +.Oo +.Fl w Ar width | +.Fl Ns Ar width +.Oc .Op Ar .Sh DESCRIPTION .Nm @@ -57,7 +60,7 @@ in bytes rather than column positions. Fold line after the last blank character within the first .Ar width column positions (or bytes). -.It Fl w Ar width +.It Fl w Ar width | Fl Ns Ar width Specifies a line width to use instead of the default 80 characters. .El .Sh EXIT STATUS Index: fold.1 =================================================================== RCS file: /cvs/src/usr.bin/fold/fold.1,v retrieving revision 1.16 diff -u -p -r1.16 fold.1 --- fold.1 28 Dec 2011 22:27:18 -0000 1.16 +++ fold.1 4 Jan 2016 19:25:18 -0000 @@ -45,7 +45,7 @@ .Nm is a filter which folds the contents of the specified files, or the standard input if no files are specified, -breaking the lines to have a maximum of 80 characters. +breaking the lines to have a maximum of 80 columns. .Pp The options are as follows: .Bl -tag -width Ds @@ -58,7 +58,7 @@ Fold line after the last blank character .Ar width column positions (or bytes). .It Fl w Ar width -Specifies a line width to use instead of the default 80 characters. +Specifies a line width to use instead of the default 80 columns. .El .Sh EXIT STATUS .Ex -std fold -- Michal Mazurek