Add a glossary entry for ecosystem

Close #4583

Author: coke

doc/Language/glossary.rakudoc

@@ -303,6 +303,13 @@ for items that have it.
 See L<operator|#Operator>. It means the type of the operator result is
 sufficiently different from its arguments that op= makes little sense.
 
+=head1 X<ecosystem|Reference,ecosystem>
+
+The module ecosystem consists of all the published modules available for Raku, which
+can be searched at L<Raku Land|https://raku.land/>. Note that different ecosystems
+based on different technologies exist, but this typically refers to the C<zef>
+ecosystem.
+
 =head1 X<Exegesis|Reference,Exegesis>
 
 A document originally written by L<TheDamian|#TheDamian>, in which he tried to explain