Selective enforcement is the ability that executors of the law (such as police officers or administrative agencies, in some cases) have to arbitrarily select choice individuals as being outside of the law. The use of enforcement discretion in an arbitrary way is referred to as selective enforcement or selective prosecution.
Historically, selective enforcement is recognized as a sign of tyranny, and an abuse of power, because it violates rule of law, allowing men to apply justice only when they choose. Aside from this being inherently unjust, it almost inevitably must lead to favoritism and extortion, with those empowered to choose being able to help their friends, take bribes, and threaten those they desire favors from. Allowing bad doctors to injure again and again or otherwise turning a blind eye on medical corruption, especially for criminal wrongdoing on the basis of having to live in the same community are examples. Each province or state investigates and disciplines doctors differently. The authorities are guilty of selective enforcement and of refusing to adequately investigate and prosecute physicians. Selective enforcement sets a bad precedent. Self regulation may predispose.
However, the converse can also be true. Police officer discretion is sometimes warranted for minor offenses, for instance where a warning to a teenager could be quite effective without putting the teen through a legal process which also reduces costs of governmental legal resources. Another example is patrol officers parked on the side of a highway for speed enforcement. It may be impractical and cost prohibitive to ticket everyone who is going any amount over the speed limit, so the officer should watch for the more egregious cases and those drivers who are showing signs of driving recklessly.