OLTP - Online Transaction Processing. An application/database designed for larger, equal, or nearly equal volumes of database inserts, updates, and deletes, as there are reads. The database is generally more (and often highly) normalized, meaning that there is less data duplication across tables and/or within tables.
OLAP - Online Analytical Processing. Essentially a data warehouse designed for larger volumes of reads than there will be inserts, updates, or deletes (often relatively very, very few deletes). Less normalized meaning that there may be duplicated data across and/or within tables in order to increase query speed at the cost of possible consistency issues due to the data duplication.
Mark this informative comment the hell up!
And smash my Karma if you want to, but the (four letter) acronyms really didn't help the article much.