# CAP theorem

CEFR C2 · Compound

Source: https://englishreference.com/word/cap-theorem
Updated: 2026-08-15

## Definition

a rule in computer science that says a database can only have two out of three things: consistency, availability, and partition tolerance. It means you have to make a choice about what is most important for your system.

For teachers: a principle in distributed computing stating that a system can provide only two of three guarantees: consistency, availability, and partition tolerance. It implies that during a network failure, a system must choose between remaining available or ensuring all data is perfectly synchronized.

## Examples

- The CAP theorem explains why some websites go offline during updates.
- When designing the new database, the engineers used the CAP theorem to decide whether to prioritize data accuracy or constant uptime.
- Architects of distributed systems must navigate the trade-offs dictated by the CAP theorem, often sacrificing immediate consistency to ensure the high availability required by global user bases.

## Usage notes

- Usually used with the definite article 'the'.

---

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.