A curl of rising vapour under two horizontal strokes standing for the sky. When the character was borrowed to write 'to say', a rain radical was piled on top to keep the weather sense — 雲 — and the simplification of 1956 threw the rain away again, returning the character to its oldest shape.
云 is the surname of Yunnan (云南, 'south of the clouds') and the word for cloud computing, 云计算. In classical Chinese 云 means 'says', which is why old texts read 子曰...人云亦云 — to say what others say — is the phrase for a parrot with no opinion.
Vapour CURLING up under the flat sky — a CLOUD.
The simplified 云 is actually the oldest form. The traditional 雲 added a rain radical on top later, and simplification simply removed it again.