Explain information retrieval with its characteristics.

Information retrieval (IR) is the process of obtaining relevant information from a large repository or database. This retrieval is based on a user's query or information need. The goal of information retrieval is to efficiently and effectively locate and deliver information that is relevant to the user's request.
For example, information retrieval is widely used in popular search engine like Google, Yahoo, Bing etc. 

Here are the key characteristics of information retrieval:
Content Organization:
IR systems organize and index vast amounts of data or documents for efficient and effective retrieval.

Query Processing:
IR systems process user queries, which can be expressed in various formats, ranging from simple keyword queries to complex Boolean expressions or natural language queries.

Relevance Ranking:
Results are ranked based on their relevance to the user's query. Various algorithms and ranking models are employed to determine the order in which results are presented to the user.

Scalability:
IR systems are designed to handle large and diverse datasets. They should be scalable to accommodate growing volumes of data without compromising performance.

Information Retrieval Models:
Different IR models, such as Boolean model, Vector Space model, and Probabilistic model, define how documents are represented and how relevance is assessed.