Microsoft Office is a bundle of Microsoft's productivity application. This includes Word, Excel, PowerPoint, Access and later Mail, Office Manager, and Outlook. The "1.x" versions of Microsoft Office were simply a marketing bundle of the standalone products sold together with no other packaging changes. Even though these were distinct applications, rather than one single monolithic program, they shared a similar user interface, integrated well together and shared the ability to embed documents from one application in the documents of another.
MS Office started out on the Macintosh, but quickly became the de-facto office suite for Windows 3.x.
Microsoft Office competed with a number of other office suites including Lotus Smartsuite, Borland/WordPerfect/Corel Office, and Star Office. Also see a complete list of Winworld's Word Processors, Spreadsheets, Databases, and Presentation programs.
Office 4.3 Professional is basically the same as Office 4.2, except it includes Microsoft Access 2.0.
Version 4.3 was sold as a "Professional" edition along side 4.2 as a "Standard" edition. This is likely because Microsoft Access, and therefore Office 4.3, was never available for the Macintosh.