At the time of this writing, Microsoft Office 365 is available at several prices and configurations and can include the following programs: Word, Excel, PowerPoint, Outlook, OneNote, Publisher, and Access.
Rather than purchase each program and then pay for upgrades, Microsoft had devised a bit of a rental model. In other words, one pays a monthly (or yearly) fee to have access to these programs on a single computer or up to five devices.
I like this model better. It allows me to have access to the programs from my computer, my laptop, my tablet and my phone. I also have online access via the web.
By saving my files "in the cloud" and can avoid the problem associated with devices that can fail or using only the computer on which I created the file.
Also, I enjoy that I always have the latest version of the software.