Lotus 1-2-3 is a spreadsheet

Spreadsheet

A spreadsheet is a computer application that simulates a paper accounting worksheet. It displays multiple cells usually in a two-dimensional matrix or grid consisting of rows and columns. Each cell contains alphanumeric text, numeric values or formulas...

 program from Lotus Software

Lotus Software

Lotus Software is a software company with headquarters in Westford, Massachusetts...

 (now part of IBM). It was the IBM PC

IBM PC

The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...

's first "killer application

Killer application

A killer application , in the jargon of marketing teams, has been used to refer to any computer program that is so necessary or desirable that it proves the core value of some larger technology, such as computer hardware, gaming console, software, or an operating system...

"; its huge popularity in the mid-1980s contributed significantly to the success of the IBM PC in the corporate environment.
The Lotus Development Corporation was founded by Mitchell Kapor, a friend of the developers of VisiCalc

VisiCalc

VisiCalc was the first spreadsheet program available for personal computers. It is often considered the application that turned the microcomputer from a hobby for computer enthusiasts into a serious business tool...

. 1-2-3 was originally written by Jonathan Sachs

Jonathan Sachs

Jonathan Sachs was the programmer who co-founded Lotus Development Corporation with Mitch Kapor in 1982 and created the first version of the Lotus 1-2-3 spreadsheet program...

, who had written two spreadsheet programs previously while working at Concentric Data Systems, Inc.