Ralph Kimball the co-founder of the data warehousing concept has defined the data warehouse as a "a copy of transaction data specifically structured for query and analysis".
Data warehousing is closely linked to OLAP - Online Analytical Processing - which relates to complex analysis of (usually aggregated, or denormalized) data in a data warehouse.
In contrast, OLTP refers to Online Transaction Processing. An OLTP database is used for day-to-day business operations and is therefore well-normalized.
See also Snowflake Schema vs. Star Schema.
Comparison chart
 | Data warehouse | OLTP |
|---|---|---|
| Introduction (from Wikipedia) | In computing, a data warehouse or enterprise data warehouse is a database used for reporting and data analysis. It is a central repository of data which is created by integrating data from one or more disparate sources. | Online transaction processing, or OLTP, refers to a class of systems that facilitate and manage transaction-oriented applications, typically for data entry and retrieval transaction processing. The term is somewhat ambiguous; some understand a "trans |
About the Author
Snowflake Schema 
calloc
Comments: Data warehouse vs OLTP