It means you’re not tied to a fixed term. You can cancel or change your mobile subscription anytime, with no penalty.
Minutes, SMS, and data included in the mobile plan are valid for national use and EU + Switzerland roaming, except special numbers (090x, 070...). Out-of-bundle calls are charged per second after the first minute. Data usage via 4G, EDGE, or GPRS is charged per KB. All prices include VAT. Private, reasonable use only, as defined [here].