The Irish Naturalisation and Immigration Service's page on biometric visas will give you more information on them. It states
You may be required to provide your biometric information as part of the visa application process.
For the purposes of the visa application process it refers to the capture of your fingerprints and, in some cases, a digital image of your face.
Countries in which visa applicants are required to provide their biometrics
Since March 2010, visa applicants residing in Nigeria (irrespective of nationality) have been required to provide their biometric information as part of the application process.
If you are resident in China or Pakistan you are required to provide your fingerprints each time you apply for a visa to Ireland.
The requirement to provide biometric information as part of the visa process is likely to be rolled out in other locations in the future.
So unless you are from one of the countries above it is unlikely that you have biometric visa.
However, if you are staying in Ireland long term, it is likely that you have either a residence permit or a category D visa in which case one of the first two points would apply to you so you wouldn't need a transit visa for the UK.