A semantic triple, or RDF triple or simply triple, is the atomic data entity in the Resource Description Framework (RDF) data model. As its name indicates, a triple is a set of three entities that codifies a statement about semantic data in the form of subject–predicate–object expressions (e.g., “Bob is 35”, or “Bob knows John”).
Subject, predicate and object
This format enables knowledge to be represented in a machine-readable way. Particularly, every part of an RDF triple is individually addressable via unique URIs — for example, the statement “Bob knows John” might be represented in RDF as:
https://example.name#BobSmith12 https://xmlns.com/foaf/0.1/knows https://example.name#JohnDoe34.
Given this precise representation, semantic data can be unambiguously queried and reasoned about.
The basic semantic triple model.
The components of a triple, such as the statement “The sky has the color blue”, consist of a subject (“the sky”), a predicate (“has the color”), and an object (“blue”). This is similar to the classical notation of an entity–attribute–value model within object-oriented design, where this example would be expressed as an entity (sky), an attribute (color) and a value (blue).
From this basic structure, triples can be composed into more complex models, by using triples as objects or subjects of other triples — for example, Mike → said → (triples → can be → objects).
Given their particular, consistent structure, a collection of triples is often stored in purpose-built databases called Triplestores.
Source: Wikipedia