All English accents can be classified as rhotic and non-rhotic. Most of the accents of England do not pronounce post-vocalic "r" and can thus be classified as non-rhotic. On the other hand, most of the accents of the United States pronounce post-vocalic "r" and can be classed as rhotic. The Jamaican accent, however, pronounces post-vocalic "r" in certain contexts but not in others. As a result, it is a semi-rhotic accent.
In words such as "father" and "turkey," Jamaican English does not pronounce the "r." In "father," the "r" is part of an unstressed syllable. Unless it is followed by a word that begins with a vowel, the "r" is not pronounced in this context. However, "turkey" is different because the "r" is part of a stressed syllable. The "r" is dropped here because it is followed by a consonant.
In words such as "here" and "occur," the "r" is pronounced. In "here," the "r" is at the end of a stressed syllable. In "occur," the context is the same. The "r" is part of a stressed syllable and is retained.
Jamaican Englsh is a variety of English that illustrates semi-rhoticity. Unlike accents of English which always preserve or drop post-vocalic "r," Jamaican English preserves it when it is the final segment of a stressed syllable but drops it when it is part of an unstressed syllable and when it is followed by another consonant. This occurs in both stressed and unstressed syllables such as "market" and "report." This feature of Jamaican English is known as semi-rhoticity.