Gsuite (g-suite, g suite) was previously called Google Apps for Work and is a bundle of software that you can use. It is a SaaS product with different (cloud-based) productivity tools and tools to collaborate within your business.
You can get a subscription, but most tools are also available for free, like you might actually use Gmail or GoogleDocs. With the monthly subscription you can have that linked to your own domain name and have more drive space available for example.
Recently it got renamed again, and now it is called Google Workplace.