There are two very different meanings of a zodiac sign. In one form of astrology, called Sidereal Astrology, the current zodiac sign is determined by the name of a constellation of stars in the ecliptic (the path of the sun, moon, and planets in the sky) that the sun apparently rises in front of. There are 12 of them and the zodiac sign is the same as the name of the constellation.

In another form of astrology, called Western Astrology, a zodiac sign is determined by how many days have elapsed since the vernal equinox. In Western Astrology each sign is exactly 1/12 of the year, so they each last 30.43 days. Western astrologers use the same names as the Sidereal astrologers, the names of the constellations on the ecliptic, but rather than worry about where the sun is actually rising in the starfield, they start the sequence of 12 signs at the same time each year, on the vernal equinox,  and make each sign last 30.43 days. So, since the exact time of the vernal equinox varies a bit each year, the start and stop dates of the 12 signs will vary slightly each year too (usually by a day or less).

If you care, In our lifetimes, the difference in these two forms of astrology makes the dates of the signs about a month different.  This is because they started out about the same 2000 years ago, but the precession of the earth on its axis [it wobble like a top in a 28,000-year cycle] causes the difference in what the starfield looks like on any particular date like the vernal equinox.

So neither form of astrology is right or wrong. You can choose to follow either. Sidereal astrology is mostly practiced in India while we use Western Astrology in the United States.