span#infobox{display:none;}
span#erster{overflow:hidden;}
div:hover span#infobox {display:block;}
<div>
<span id="erster">TEXT</span>
<span id="infobox">Hier stehen Infos</span>
</div>
span#infobox{display:none;}
span#erster{overflow:hidden;}
div:hover span#infobox {display:block;}
<div>
<span id="erster">TEXT</span>
<span id="infobox">Hier stehen Infos</span>
</div>