Writing 255.255.255.0 every time gets old. CIDR (Classless Inter-Domain Routing) is the short form. You count how many bits of the 32-bit address belong to the street, then write that count after a slash. 192.168.10.0/24 means the first twenty-four bits are network. That is the same street line as mask 255.255.255.0. A /16 matches 255.255.0.0. A /8 matches 255.0.0.0.
Prefix length is just that slash number. It does not change what the address is. It only says how many lamps on the left are street lamps. Longer prefix, smaller street, fewer house numbers. Shorter prefix, bigger street. Classful A/B/C thinking pretended the split always fell on octet boundaries. CIDR lets the split fall on any bit, which is how real networks get sized to the job instead of to a 1980s habit.
Basically, when you see slash twenty-four, translate it: twenty-four bits of street, eight bits of house, up to 254 usable hosts on that street (all-zeros and all-ones are reserved). Students sometimes type /24 into a mask field and watch a lab reject it. Same idea, two spellings. Learn both. The mask is the lamps. The prefix is the count.
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