In simple terms it is a relational database that allows the development of processes to fit with the client needs.
In reality it is a tool that alows me to take the requirements that are given to me and develop the processes needed to complete the tasks by the end users in the most practical way possible. So the development of the front end (or interface) is paramount for the smooth running of the in house process to achieve the business aims without making it too complicated for the end user to understand or use.
It is a rapid application development platform that allows me to prototype the end application before delving into the way that the fields and records interact with each other, so that the way that you use the application developed has greater importance than the way that FileMaker works internally.
I have been using and develping within FileMaker since its inception as a product in the original Claris form. From simple projects up to a full company wide application can be custom built from FileMaker alowing a degree of flexability to ensure that the clients needs are fulfilled.