Convenience samples are frequently used (as implied by Ette Etuk's answer), since they are much easier to obtain than probability samples (e.g., simple random sample or stratified random sample). However, the concern is how confident you can be that your sample is genuinely representative of the target population. Whether results obtained from your convenience sample would generalize to that population is therefore an unknown.
In any event, be sure to indicate the method you used to obtain your sample in your research write-up.
It sometimes depends on your objectives, but to my knowledge you can use convenience sampling and avoid the shibboleth that you cannot generalize your findings to the population sampled by doing the right statistics and selecting the appropriate research design. Please see the links below for more information.
Article Mixed-effects modeling with crossed random effects for subje...
Article The Language-as-Fixed-Effect Fallacy: A Critique of Language...
Yes, convenience sampling is allowed in quantitative research. What is crucial is, since convenience sampling is prone to the challenge of representativeness, the researcher must ensure the sample is relatively a reflection of the population of the study.
Convenience sampling techniques and similar nonprobability sampling methods can be applied in qualitative research design. The only limitation associated with the use of such is the fact that the outcomes of the research involved are not generalizable to the research population.
To the best of my knowledge in research, I will Say Yes, it means the people that is available to you during the distribution of your questionnaire will be your participants or responded, they are the convenient respondent of your study. See it this way, you are in the Canteen and you make use of the people that coming during your stay in the canteen as your respondents. It can be used in quantitative
Etikan, I., Musa, S. A., & Alkassim, R. S. (2016). Comparison of convenience sampling and purposive sampling. American journal of theoretical and applied statistics, 5(1), 1-4.