This is the 5557th most frequent German word.
besuchende
"Visiting" or "visitors" (depending on context).
In this sentence, 'besuchende' is used as a noun derived from a present participle. It refers to people who are visiting, i.e., 'visitors.'
Besuchende der Ausstellung müssen sich registrieren.
Visitors to the exhibition must register.
Here, 'besuchenden' is an adjective derived from the present participle, describing the experts' action or state of visiting.
Die besuchenden Experten werden sich morgen treffen.
The visiting experts will be meeting tomorrow.
In this usage, 'besuchenden' functions as an attributive adjective, describing the groups who are in the act or status of visiting the museum.