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Given the following plain TeX snippet and it's output:
hallo werld
{\catcode`\ =12
hallo wereld}
{\tt
hallo wereld}
{\tt\catcode`\ =12
hallo wereld}
The command \catcode`\ =12 changes the category of the space character to "Other". This will make TeX display it.
The space glyph in a typewriter typeface looks familiar. However, the glyph shown in the default typeface I don't recognize.
Out of curiosity, does it have a name? And what is it used for?
TeX doesn't use a real character from the current font for spaces, so Knuth decided to fill also the slot usually reserved for it with a rarely used glyph: the slash for producing the "Polish suppressed ell" ł. Here are the relevant lines in plain.tex
\def\l{\char32l}
\def\L{\leavevmode\setbox0\hbox{L}\hbox to\wd0{\hss\char32L}}
This is also supplemented by a kerning entry in the TFM file:
(LIGTABLE
(LABEL O 40)
(KRN C l R -0.277779)
(KRN C L R -0.319446)
(STOP)
...
Since the character has width 0.277779pt, when it comes before a lowercase "l", its width is compensated for.
In the cmtt10 font (and the other typewriter type fonts), the slot is filled with a "visible space".
It looks like the slash on U+2422 (BLANK SYMBOL): ␢. Since LaTeX has been known to overlay slashes on regular characters (e.g., the symbol produced by \hbar), I bet the underlying b was erased or omitted.
