Extracted from the website of Buddhist Vajrayana Charity Funds Association and translated (阿卡是甚麼人) into English:

What kind of a person is ‘Ah Ka’?

‘Ah Ka’ is the Chinese transliteration of a respectful form of address (a way of showing respect) used by the people of Qinghai to address those in the Buddhist community. A more accurate explanation is that it is a name for those in the Tibetan Buddhist community in ‘Amdo Tibetic Language(安多藏語)’.

‘Lama’ means ‘Buddhist monk’ in Tibetan language. Within China, in places such as Inner Mongolia, Qinghai and Tibet, everyone addresses the Tibetan Buddhist community as ‘lama’, meaning Guru or virtuous friend. There are two different meanings for virtuous friend: one is the external virtuous friend (the outer Guru), and the other is the internal virtuous friend (the inner Guru). Therefore, strictly speaking, not every monk can be called a lama.

When you see a monk from a Chinese Buddhist temple, such as monk so and so, you cannot directly call him by his name; instead you must call him Great Master so and so or Dharma Master so and so. Hence, Lama is a title and Ah Ka is a respectful form of address (addressing somebody respectfully), such as calling Lama so and so as Ah Ka so and so.

In Tibetan Buddhism, Rinpoche/Ren-Bo-Qie (transliteration) means precious one/jewel (The word consists of rin‘value’ and po‘nominative suffix’ and che‘big’), more commonly known as the Living Buddha; Khenpo means host; and Lama means monk. Only those that are highly respected, such as Rinpoche/Ren-Bo-Qie and Khenpo, can be called Lama, and the people of Qinghai call the ordinary monk as Ah Ka.

Guru means the Superior Master. Speaking from the perspective of a practitioner, Guru Lama is a lama who is the immediate teacher of the practitioner. A Rinpoche may not necessarily be a monk, but Lama Rinpoche is a Rinpoche who has already become a monk. As for a practitioner, Guru Rinpoche is a Rinpoche who is the personal teacher of the practitioner; and Guru Lama Rinpoche is a Lama Rinpoche who is the direct teacher of the practitioner.