Yes, in our Singapore system, as well as the US, since its modelled from there mixed.
There is ONLY one professor in that field in a university. That professor is supposed to be the best in that field and will chart and provide research direction for the university in that field of research. This title is bestowed upon him and is certified as a permanent tenure.

Normally, for the same field, there will be 2 to 3 associate professors who will aid the Professor in that field. These positions can/may be earned through seniority, no. of publications, depth of knowledge, appraisals, universal acknowledgement of his work, etc. They may or may not be permanent tenure positions, but most definitely are.

The rest are asst. professors, followed by Dr. (acad), research fellows.....these are Ph.Ds, but are younger, most prob. about <5 to 10 years of experience after their Ph.D. Some might have followed leading research scientist before, etc. These are jobs, thus they are NOT tenure positions. That is, you sign on per 4 years, etc...sort of contractual basis.

Next, are Research associates, research assistants, Research scholars, etc... who do NOT yet hold a Ph.D. but are unable some abled professors or assc. professor so as to obtain a Ph.D.

Associates, Assistants meant that they are not yet able to perform independent research to their potential and write up research journals etc, so the Assoc or Prof is their supervisors.
Other exceptional positions in academia are Honorary Professor, Temasek Professor, Visiting Professor, and Emeritus Professor.
Honorary - a doctor through years of experience in the industry >30years !! ...therefore university decides to award him/her in a ceremony...could also be contribution in a world accident, found a world cure, give money to charity etc.

Temasek - currently in Singapore there is only 3 such professors, SUPPOSED TO Chart direct for Singapore in terms of research field, to make singapore competitive and earn money for Singapore! T.Profs control/is in charge of Professors in both NUS/NTU!

Dun even to ask about their salaries.

Visiting - On sabatical to another University, and is teaching/doing research for 6months to 1 year.
Emeritus - Already retired, given the supreme honorary title due to contribution in the arena. And provide consultation and suggestions to Professors and Assoc. Professors!
There is a sub position called Senior Lecturer....these may/may Not be professors, their could have a Masters degree, basic degree, double-masters, who have been teaching in a university for >5 years. They may subsequently be given a scholarship overseas to get their Ph.D. and then come back as a Doctor or Asst. Prof. in the future. These are common 5-10 years back as some cannot get the money to study or go overseas, so their stayed back in univ. to teach and earn money etc.