Computer programs; also called applications, that perform a specific function. Software is generally installed on hardware (your computer) as an interface to perform tasks and increase productivity.
Examples are Microsoft Office (e.g. Word, Ecxel, Powerpoint, Outlook, etc), browsers (e.g. Chrome, Edge, Firefox, etc), inventory systems, reservation systems (e.g. RMS) or accounting systems (e.g. MYOB, Xero, etc).
It is important that you install any available updates to minimise interruptions of your business operations. Software manufacturers regularly provide you with updates to increase the security of your applications and to improve their performance.
It is more and more common to access software through your browser (SaaS, software as a service). Examples for this are your online banking, online accounting, online bookings etc.
The advantage of SaaS are that the software is updated by the manufacturer.
In most cases you need a licence to install/use computer programs. Depending on the manufacturer this can be a onetime fee or a monthly subscription fee. Common software suites on a subscription model are Microsoft Office 365, G Suite, MYOB, etc.