For my link archive (please check the page as by now the table might have changed from what I quote below) [Wayback/Archive] Unicode spaces and the WordPress classic editor might have mangled it.
I like the table as it embeds the spaces between foo and bar so it easy to copy paste them to code or documentation.
Space characters and “zero-width spaces” in Unicode Code Name of the character Sample Width of the character U+0020 SPACE foo bar Depends on font, typically 1/4 em, often adjusted U+00A0 NO-BREAK SPACE foo bar As a space, but often not adjusted U+1680 OGHAM SPACE MARK foo bar Unspecified; usually not really a space but a dash U+180E MONGOLIAN VOWEL SEPARATOR foobar 0 U+2000 EN QUAD foo bar 1 en (= 1/2 em) U+2001 EM QUAD foo bar 1 em (nominally, the height of the font) U+2002 EN SPACE (nut) foo bar 1 en (= 1/2 em) U+2003 EM SPACE (mutton) foo bar 1 em U+2004 THREE-PER-EM SPACE (thick space) foo bar 1/3 em U+2005 FOUR-PER-EM SPACE (mid space) foo bar 1/4 em U+2006 SIX-PER-EM SPACE foo bar 1/6 em U+2007 FIGURE SPACE foo bar “Tabular width”, the width of digits U+2008 PUNCTUATION SPACE foo bar The width of a period “.” U+2009 THIN SPACE foo bar 1/5 em (or sometimes 1/6 em) U+200A HAIR SPACE foo bar Narrower than THIN SPACE U+200B ZERO WIDTH SPACE foobar 0 U+202F NARROW NO-BREAK SPACE foo bar Narrower than NO-BREAK SPACE (or SPACE), “typically the width of a thin space or a mid space” U+205F MEDIUM MATHEMATICAL SPACE foo bar 4/18 em U+3000 IDEOGRAPHIC SPACE foo bar The width of ideographic (CJK) characters. U+FEFF ZERO WIDTH NO-BREAK SPACE foobar 0
–jeroen