1. Historically, a "confessional church" is a body that ascribes to a denominational standard, e.g., Helvetic, Belgic, LBCF, Westminster, Savoy, etc. These churches confess that the Bible is the sole and final authority in all matters of faith (doctrine) and practice... and that the Standard/Confession is their secondary authority in all that it says which is consistent with biblical teaching.

2. In more modern times, it can mean that a denomination or individual church ascribes to a confession/standard which they have written themselves. Typically, these type of confessions are very simple and pale in comparison to the historical confessions which came about after the Protestant Reformation as were all those mentioned above. Precision isn't one of their attributes and most are contrary to the doctrines of the reformational confessions.

3. Lastly, EVERY church is confessional in the sense that the individual church has a set of beliefs, whether written or unwritten to which members are required to acknowledge as truth and voluntarily agree to submit to and be disciplined if broken. You will see these written 'confessions' on most church websites, usually designated as "What We Believe", or something similar.

#1 is, or was, the understood meaning of a "Confessional Church".

One more thing I feel I would be reticent if not mentioned. A denomination/church can claim to be confessional but that does not guarantee that they accept their Standard(s) as a binding secondary authority, or consistently teach and live by them, e.g., the PCUSA retains the Westminster Standards as part of their denomination but openly disagrees with most of what those Standards teach. They are valuable as part of history and not much more. There are other confessional denominations who haven't gone as far as the PCUSA in denying the majority of the teachings of their respective Standard(s), but they are slowly going in that direction. This is not unusual historically. Many, if not most of the major Reformed denominations are in our day are traveling down that road to one degree or another and will eventually become just another "used to be confessional" church. Out of them will be those who sooner or later recognize the seriousness of what is happening, leave and start a new denomination/church. Revelation chapters 2&3 is an accurate description of where the visible church is today. The majority have gone astray in various ways but a few have remained faithful. The question that needs to be asked is, "Where is MY church/denomination among those described in Revelation?" Most people play ostrich and refuse to take seriously the signs of impending apostasy around them. And that is one of the major contributions to the demise of their church/denomination.