The basis for astrological predictions for an individual is the particular configuration of the planets as viewed from his (or her) birthplace at the time of his (or her) birth. The form (or format) in which the planetary positions in the space surrounding the place at the time of birth
presented is called a horoscope or a birth chart.
There are different types of formats in use today to describe the planetary positions at a particular time in the space surrounding the place where a person is born. But they all convey the same basic information on which an astrologer bases his predictions.
Incidentally, the meaning of the term "horoscope", as it is being used today, is misleading. For example, the "horoscope" we read in paper today doesn't mean anything that I just described. What we read in paper today in the horoscope column is a very general prediction provided by an astrologer for all zodiac signs; each corresponding to the zodiac sign occupied by the Sun at the time of birth based on the moving zodiac system. In other countries, particularly in South East Asia, where the fixed zodiac system is popular, the similar predictions are based on the zodiac signs either occupied by the Sun or the Moon (the latter being more popular) at the time of birth. However, regardless of the zodiac system used, it is important to recognize that these predictions are based on the effects of only one planet (either the Sun or the Moon) while the effects of other planets totally ignored. As a result, it's not surprising that most of the times these columns become the targets of fun and ridicule as they are inadequate in delivering the individual predictions. In other words, you can't divide the whole world's population in twelve groups and successfully impose the twelve different predictions on them based solely on the Sun or Moon's position in their birth charts.