In the broadest sense of the word, aggregation means collecting and combining of data horizontally, vertically and chronologically and then expressed in summary form to be used for statistical analysis. In the more technical sense, aggregation is a special kind association that specified a part of whole relationship between the component part and the while.

As opposed to ordinary association, aggregation is more of an asymmetric relationship and transitive relationship. Aggregation also implies a stronger coupling and behavior is normally propagated across an aggregation.

In relational database, aggregation refers to combination of data from different records. For example, sales records and corporate income from one or several branches can be reported using aggregation. The process of aggregation of various data from several sources can be done by executive one database query.

An example of the use of aggregation in internet advertising is to get information and trends on a particular group based on a specific variable like income, age and profession. The information gathered and the patterns spotted may be used for website personalization. This is useful when a company wants to choose content to specific users and advertising can be directly targeted to them. For instance, a site that is selling a movies and music on CDs and DVDs may recommend or advertise genres based on the age of the user and the data aggregate for the group.

Online analytic processing (OLAP) is a particular method used in data warehouses which uses a simple type of data aggregation for the marketer to use an online reporting strategy to process gathered information.

Data aggregation can be used for personal data aggregation services to offer a user one point for collection of his personal information from other websites. The user can use a single master personal identification number (PIN) which he can use to access a variety of other accounts like airlines, clubs and financial institutions. This kind of aggregation is often called "screen scraping".

Aggregation services are offered as a standalone or may be in conjunction with other services like bills payment and tracking of portfolio which is provided by other specialized websites. Many big and stable companies that use the internet for web presence and transactions offer aggregation services to entice visitors.

During the course of time, large amounts of aggregated account data from provider to server are transferred and may develop into a comprehensive database of user profiles with details of balances, securities transactions, credit information and other information. Privacy and security become a major issue but there are independent companies offering these related services.

Because of the possibility of liabilities that may arise from activities related to data aggregations such as security issues and infringement of intellectual property rights, aggregators may agree on a data feed arrangement at the discretion of the end user or customers. This may involve using an Open Financial Exchange (OFX) standard in requesting and delivering the information to the customer. This agreement will provide an opportunity for institutions to protect the interest of their customers’ interest and for aggregators to come up with more robust services. Screen scrapping without the content provider’s consent can lead to allowing subscribers to see any account opened through a single website.

Another form of aggregation which is ubiquitous in the internet today is RSS syndication. RSS, which stands for Really Simple Syndication, is a small database that contains headlines and description of news or other information on a website. RSS gets aggregate data from several specified sources from other websites and they are automatically updated at a central point in one’s syndicated website. Contents from RSS are read using a feed reader or an aggregator.