Uptime refers to the amount of time your website is operational and accessible to visitors on the internet. It's typically expressed as a percentage, representing the proportion of time your site is up versus down over a given period, such as a month or a year.

For example, 99.9% uptime (often called "three nines") means your website can be down for up to 8.76 hours per year without breaching the guarantee. Higher percentages mean better reliability:

• 99% uptime: Allows ~3.65 days of downtime/year
• 99.9% uptime: Allows ~8.76 hours of downtime/year
• 99.99% uptime ("four nines"): Allows ~52.6 minutes of downtime/year

Uptime is critical because every minute your site is offline can result in:

• Lost revenue from sales or ads
• Damaged reputation and user trust
• Lower search engine rankings (Google penalizes unreliable sites)
• Frustrated visitors who may never return

When choosing a web host, look for providers offering at least 99.9% uptime guarantees with service level agreements (SLAs) that provide compensation if they fail to meet their promise. Remember that no host can guarantee 100% uptime due to unavoidable maintenance and unforeseen issues, but premium hosts invest in redundant systems to maximize reliability.

You can monitor your website's uptime using free tools like UptimeRobot or StatusCake that alert you immediately when your site goes down. For mission-critical websites, consider using multiple hosting providers or a content delivery network (CDN) to minimize downtime impact.