UTC (Coordinated Universal Time) is the primary time standard by which the world regulates clocks and time. It is similar to GMT (Greenwich Mean Time) but is more precisely defined by atomic clocks. UTC is the time standard used across the internet and for international communications and aviation.

Timezones are regions of the globe that observe a uniform standard time. They are generally defined as offsets from UTC, typically in whole-hour increments. For example, Eastern Standard Time (EST) is UTC-5, meaning it is 5 hours behind UTC. Timezones were created to standardize time across large geographical areas and are often influenced by political boundaries as well as geographical ones.

A Unix timestamp (also known as Unix time or POSIX time) represents the number of seconds that have elapsed since January 1, 1970, at 00:00:00 UTC, not counting leap seconds. It's widely used in computer systems and programming as a standardized way to track time regardless of timezone. Unix timestamps make it easy to calculate time differences and are independent of calendar conventions.

The accuracy of this clock depends on your device's system clock and internet connection. While we strive to display the most accurate time possible, there may be slight variations due to network latency or your device's clock synchronization. For most everyday purposes, the time displayed should be accurate within a few seconds of the actual time. For applications requiring millisecond precision, specialized time servers should be used.

ISO 8601 is an international standard for representing dates and times. It follows the format YYYY-MM-DDTHH:MM:SS.sssZ, where: YYYY-MM-DD represents the date (year, month, day), T is a separator between date and time, HH:MM:SS.sss represents the time (hours, minutes, seconds, and milliseconds), Z indicates that the time is in UTC (or an offset can be specified, like +01:00). This format eliminates ambiguity in international communications and is widely used in computing.

Daylight Saving Time (DST) is the practice of advancing clocks during warmer months so that darkness falls later each day according to the clock. Typically, regions that observe DST adjust clocks forward one hour in the spring ("spring forward") and adjust them backward in the autumn ("fall back"). The main purpose is to make better use of daylight during the evening hours. Not all countries observe DST, and the start and end dates vary by region.

To convert time between timezones, you need to: 1) Determine the UTC offset for both the source and target timezones, 2) Convert the source time to UTC by adding or subtracting its offset, 3) Convert from UTC to the target timezone by adding or subtracting the target timezone's offset. For example, to convert 3:00 PM in New York (UTC-5) to London time (UTC+0), you would add 5 hours to get 8:00 PM London time. Remember to account for Daylight Saving Time if applicable, as it can change the UTC offset temporarily.