What does a slot mean in Catalyst switches?

[dalakshm]

"I see description like x slot yRU chassis "

What does x slot represents here?

[Joseph W. Doherty]

Generally a generic way of describing where a module or card are installed in the device. Sometime "large" modules or cards, themselves, can have other components installed in them as modules.

[Scott Hodgdon]

dalakshm,

When we say "x slot yRU chassis", we mean this:

x = the number of slots in a chassis. 

y = the number of Rack Units (RU) the chassis takes in a rack

For example, if you look at https://www.cisco.com/c/en/us/products/collateral/switches/catalyst-9400-series-switches/data_sheet-c78-739053.html , you see in Table 1 that a C9404R is Total Number of slots = 4. In Table 6 you see C9404R is Rack Units (RU) = 6.

So we might say that the Catalyst 9404 is 4 slots and 6 RU. Notice in Table 1 that some slots are reserved for Supervisor Engines and some are for Linecards.