The user experience is made up of all the interactions a person has with your brand, company, or organization. This may include interactions with your software, your web site, your call center, an advertisement, with a sticker on someone else’s computer, with a mobile application, with your Twitter account, with you over email, maybe even face-to-face. The sum total of these interactions over time is the user experience.
All of these touch-points are important parts of the larger system.