The IEC 60529 IP code summarises the sealing of an enclosure in two digits. The first, 0 to 6, covers protection against solid bodies and dust: 5 means dust-protected and 6 means fully dust-tight. The second, 0 to 9, covers water: 4 is splashing, 5 water jets, 6 powerful jets and 7 temporary immersion to one metre for 30 minutes.
So IP54 describes equipment protected against dust in harmful quantity and against splashing from any direction; IP65, dust-tight and resistant to water jets; IP67, dust-tight and able to survive immersion.
On field test equipment the rating almost always refers to the case closed, not to the instrument in use with cables connected. That is an important nuance when comparing datasheets: an IP67 with the lid closed and an IP54 in operation describe different situations.