A content management system is the back end of a website where you can upload content, manage your products and sometimes make small design changes. You can have your website built using an off the shelf content management system such as WordPress or you can have a bespoke one.
There are many advantages to using a bespoke or custom CMS, but if you are a small business who is looking to stay small, then it may not be recommended. A customer CMS system will often cost a lot more than an off the shelf CMS and therefore as a small business, you may find that you do not use much of the additional functionality and end up paying well over the odds for what you need and want.
Bespoke CMS systems are perfect for business who are looking to add functionality to their website quite often and need to be able to adapt the system if their website is going to be quite unique. Often complex ecommerce websites will need to be built with a bespoke CMS system. The only issue with this is if you want to move the website to another company you will not be allowed to take the CMS with you so will need to have it integrated into another content management system which can cost time and money.