PureMatrimony.com isn't for everyone, it is exclusively for Muslims who are serious about practising their deen, and our measurement of this is the salah. This is based on the Prophetic tradition, "the difference between a Muslim, and kufr and shirk is the salah" [Sahih Muslim, Book 1, No 147]
By confirming that you perform your prayers on a daily basis, it serves as an indication that you are not neglectful in your duties toward Allah – an important consideration for any practising single Muslim who wants to find a likeminded spouse.
We appreciate that many people have difficulty in praying 5x a day on time. Some find Fajr exceptionally difficult, but make up for it afterwards. We're not seeking to exclude those people who are aware and acknowledge the importance of the prayer. We are just seeking to exclude those who don't care about prayer at all.
If you feel you are not neglectful towards your daily prayers (i.e. you pray daily, and the ones you miss you still make them up), then insha'Allah you can confirm you pray every day. If the prayer is more of an occasional thing for you, then this wouldn't count.
We don't put any particular limit on the definition. For the moment, it's left up to your own interpretation as only you and Allah SWT know your own circumstances. This is why we ask in the second question for you to swear by Allah SWT that you're being truthful in what you say - and we expect honesty throughout all interaction on the site, not just for this initial question.