# CIDR

Source: https://englishreference.com/word/cidr
Updated: 2026-08-27

## Senses

### 1. networking notation

noun · CEFR C2 · Technical

Stands for Classless Inter-Domain Routing. It is a way to write an IP address and its network mask together, like 192.168.1.0/24.

For teachers: Abbreviation for Classless Inter-Domain Routing. A standard for IP address allocation and routing that uses variable-length subnet masking to improve address space efficiency.

- The network administrator assigned a new CIDR block to the office wifi.
- By implementing CIDR notation, the engineering team was able to consolidate multiple routing table entries into a single prefix, significantly reducing overhead.

Usage: Usually functions as a noun or an attributive noun modifying 'block', 'notation', or 'address'.

Teaching tip: This is a highly specialized term used by IT professionals and network engineers; most general English learners will never encounter it.

## Examples

- The network administrator assigned a new CIDR block to the office.
- Using CIDR notation allows engineers to define a range of IP addresses with a single prefix and a slash.
- The introduction of CIDR in 1993 was essential for slowing the exhaustion of IPv4 addresses and preventing the explosion of routing tables across the global internet backbone.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.